diff --git a/oracle/callees.go b/oracle/callees.go
index afd8d83f..1e0d65e1 100644
--- a/oracle/callees.go
+++ b/oracle/callees.go
@@ -20,28 +20,28 @@ import (
 //
 // TODO(adonovan): if a callee is a wrapper, show the callee's callee.
 //
-func callees(o *oracle) (queryResult, error) {
+func callees(o *Oracle, qpos *QueryPos) (queryResult, error) {
 	// Determine the enclosing call for the specified position.
 	var call *ast.CallExpr
-	for _, n := range o.queryPath {
+	for _, n := range qpos.path {
 		if call, _ = n.(*ast.CallExpr); call != nil {
 			break
 		}
 	}
 	if call == nil {
-		return nil, o.errorf(o.queryPath[0], "there is no function call here")
+		return nil, o.errorf(qpos.path[0], "there is no function call here")
 	}
 	// TODO(adonovan): issue an error if the call is "too far
 	// away" from the current selection, as this most likely is
 	// not what the user intended.
 
 	// Reject type conversions.
-	if o.queryPkgInfo.IsType(call.Fun) {
+	if qpos.info.IsType(call.Fun) {
 		return nil, o.errorf(call, "this is a type conversion, not a function call")
 	}
 
 	// Reject calls to built-ins.
-	if b, ok := o.queryPkgInfo.TypeOf(call.Fun).(*types.Builtin); ok {
+	if b, ok := qpos.info.TypeOf(call.Fun).(*types.Builtin); ok {
 		return nil, o.errorf(call, "this is a call to the built-in '%s' operator", b.Name())
 	}
 
diff --git a/oracle/callers.go b/oracle/callers.go
index 37549978..01f827be 100644
--- a/oracle/callers.go
+++ b/oracle/callers.go
@@ -17,20 +17,20 @@ import (
 //
 // TODO(adonovan): if a caller is a wrapper, show the caller's caller.
 //
-func callers(o *oracle) (queryResult, error) {
-	pkg := o.prog.Package(o.queryPkgInfo.Pkg)
+func callers(o *Oracle, qpos *QueryPos) (queryResult, error) {
+	pkg := o.prog.Package(qpos.info.Pkg)
 	if pkg == nil {
-		return nil, o.errorf(o.queryPath[0], "no SSA package")
+		return nil, o.errorf(qpos.path[0], "no SSA package")
 	}
-	if !ssa.HasEnclosingFunction(pkg, o.queryPath) {
-		return nil, o.errorf(o.queryPath[0], "this position is not inside a function")
+	if !ssa.HasEnclosingFunction(pkg, qpos.path) {
+		return nil, o.errorf(qpos.path[0], "this position is not inside a function")
 	}
 
 	buildSSA(o)
 
-	target := ssa.EnclosingFunction(pkg, o.queryPath)
+	target := ssa.EnclosingFunction(pkg, qpos.path)
 	if target == nil {
-		return nil, o.errorf(o.queryPath[0], "no SSA function built for this location (dead code?)")
+		return nil, o.errorf(qpos.path[0], "no SSA function built for this location (dead code?)")
 	}
 
 	// Run the pointer analysis, recording each
diff --git a/oracle/callgraph.go b/oracle/callgraph.go
index 6ebe1912..c8cdd680 100644
--- a/oracle/callgraph.go
+++ b/oracle/callgraph.go
@@ -25,7 +25,7 @@ import (
 //
 // TODO(adonovan): elide nodes for synthetic functions?
 //
-func callgraph(o *oracle) (queryResult, error) {
+func callgraph(o *Oracle, _ *QueryPos) (queryResult, error) {
 	buildSSA(o)
 
 	// Run the pointer analysis and build the complete callgraph.
@@ -35,6 +35,7 @@ func callgraph(o *oracle) (queryResult, error) {
 
 	// Assign (preorder) numbers to all the callgraph nodes.
 	// TODO(adonovan): the callgraph API should do this for us.
+	// (Actually, it does have unique numbers under the hood.)
 	numbering := make(map[pointer.CallGraphNode]int)
 	var number func(cgn pointer.CallGraphNode)
 	number = func(cgn pointer.CallGraphNode) {
@@ -70,6 +71,8 @@ Some nodes may appear multiple times due to context-sensitive
  treatment of some calls.
 `)
 
+	// TODO(adonovan): compute the numbers as we print; right now
+	// it depends on map iteration so it's arbitrary,which is ugly.
 	seen := make(map[pointer.CallGraphNode]bool)
 	var print func(cgn pointer.CallGraphNode, indent int)
 	print = func(cgn pointer.CallGraphNode, indent int) {
diff --git a/oracle/callstack.go b/oracle/callstack.go
index 16516b6d..6a5f4323 100644
--- a/oracle/callstack.go
+++ b/oracle/callstack.go
@@ -22,21 +22,21 @@ import (
 // TODO(adonovan): permit user to specify a starting point other than
 // the analysis root.
 //
-func callstack(o *oracle) (queryResult, error) {
-	pkg := o.prog.Package(o.queryPkgInfo.Pkg)
+func callstack(o *Oracle, qpos *QueryPos) (queryResult, error) {
+	pkg := o.prog.Package(qpos.info.Pkg)
 	if pkg == nil {
-		return nil, o.errorf(o.queryPath[0], "no SSA package")
+		return nil, o.errorf(qpos.path[0], "no SSA package")
 	}
 
-	if !ssa.HasEnclosingFunction(pkg, o.queryPath) {
-		return nil, o.errorf(o.queryPath[0], "this position is not inside a function")
+	if !ssa.HasEnclosingFunction(pkg, qpos.path) {
+		return nil, o.errorf(qpos.path[0], "this position is not inside a function")
 	}
 
 	buildSSA(o)
 
-	target := ssa.EnclosingFunction(pkg, o.queryPath)
+	target := ssa.EnclosingFunction(pkg, qpos.path)
 	if target == nil {
-		return nil, o.errorf(o.queryPath[0],
+		return nil, o.errorf(qpos.path[0],
 			"no SSA function built for this location (dead code?)")
 	}
 
@@ -74,19 +74,21 @@ func callstack(o *oracle) (queryResult, error) {
 	}
 
 	return &callstackResult{
+		qpos:      qpos,
 		target:    target,
 		callstack: callstack,
 	}, nil
 }
 
 type callstackResult struct {
+	qpos      *QueryPos
 	target    *ssa.Function
 	callstack []pointer.CallSite
 }
 
 func (r *callstackResult) display(printf printfFunc) {
 	if r.callstack != nil {
-		printf(false, "Found a call path from root to %s", r.target)
+		printf(r.qpos, "Found a call path from root to %s", r.target)
 		printf(r.target, "%s", r.target)
 		for _, site := range r.callstack {
 			printf(site, "%s from %s", site.Description(), site.Caller().Func())
diff --git a/oracle/describe.go b/oracle/describe.go
index 143c7e4c..2c30823c 100644
--- a/oracle/describe.go
+++ b/oracle/describe.go
@@ -33,25 +33,25 @@ import (
 //
 // All printed sets are sorted to ensure determinism.
 //
-func describe(o *oracle) (queryResult, error) {
+func describe(o *Oracle, qpos *QueryPos) (queryResult, error) {
 	if false { // debugging
-		o.fprintf(os.Stderr, o.queryPath[0], "you selected: %s %s",
-			importer.NodeDescription(o.queryPath[0]), pathToString2(o.queryPath))
+		o.fprintf(os.Stderr, qpos.path[0], "you selected: %s %s",
+			importer.NodeDescription(qpos.path[0]), pathToString2(qpos.path))
 	}
 
-	path, action := findInterestingNode(o.queryPkgInfo, o.queryPath)
+	path, action := findInterestingNode(qpos.info, qpos.path)
 	switch action {
 	case actionExpr:
-		return describeValue(o, path)
+		return describeValue(o, qpos, path)
 
 	case actionType:
-		return describeType(o, path)
+		return describeType(o, qpos, path)
 
 	case actionPackage:
-		return describePackage(o, path)
+		return describePackage(o, qpos, path)
 
 	case actionStmt:
-		return describeStmt(o, path)
+		return describeStmt(o, qpos, path)
 
 	case actionUnknown:
 		return &describeUnknownResult{path[0]}, nil
@@ -305,11 +305,11 @@ func findInterestingNode(pkginfo *importer.PackageInfo, path []ast.Node) ([]ast.
 // to the root of the AST is path.  It may return a nil Value without
 // an error to indicate the pointer analysis is not appropriate.
 //
-func ssaValueForIdent(o *oracle, obj types.Object, path []ast.Node) (ssa.Value, error) {
+func ssaValueForIdent(prog *ssa.Program, qinfo *importer.PackageInfo, obj types.Object, path []ast.Node) (ssa.Value, error) {
 	if obj, ok := obj.(*types.Var); ok {
-		pkg := o.prog.Package(o.queryPkgInfo.Pkg)
+		pkg := prog.Package(qinfo.Pkg)
 		pkg.Build()
-		if v := o.prog.VarValue(obj, pkg, path); v != nil {
+		if v := prog.VarValue(obj, pkg, path); v != nil {
 			// Don't run pointer analysis on a ref to a const expression.
 			if _, ok := v.(*ssa.Const); ok {
 				v = nil
@@ -328,8 +328,8 @@ func ssaValueForIdent(o *oracle, obj types.Object, path []ast.Node) (ssa.Value,
 // return a nil Value without an error to indicate the pointer
 // analysis is not appropriate.
 //
-func ssaValueForExpr(o *oracle, path []ast.Node) (ssa.Value, error) {
-	pkg := o.prog.Package(o.queryPkgInfo.Pkg)
+func ssaValueForExpr(prog *ssa.Program, qinfo *importer.PackageInfo, path []ast.Node) (ssa.Value, error) {
+	pkg := prog.Package(qinfo.Pkg)
 	pkg.SetDebugMode(true)
 	pkg.Build()
 
@@ -345,7 +345,7 @@ func ssaValueForExpr(o *oracle, path []ast.Node) (ssa.Value, error) {
 	return nil, fmt.Errorf("can't locate SSA Value for expression in %s", fn)
 }
 
-func describeValue(o *oracle, path []ast.Node) (*describeValueResult, error) {
+func describeValue(o *Oracle, qpos *QueryPos, path []ast.Node) (*describeValueResult, error) {
 	var expr ast.Expr
 	var obj types.Object
 	switch n := path[0].(type) {
@@ -353,7 +353,7 @@ func describeValue(o *oracle, path []ast.Node) (*describeValueResult, error) {
 		// ambiguous ValueSpec containing multiple names
 		return nil, o.errorf(n, "multiple value specification")
 	case *ast.Ident:
-		obj = o.queryPkgInfo.ObjectOf(n)
+		obj = qpos.info.ObjectOf(n)
 		expr = n
 	case ast.Expr:
 		expr = n
@@ -362,8 +362,8 @@ func describeValue(o *oracle, path []ast.Node) (*describeValueResult, error) {
 		return nil, o.errorf(n, "unexpected AST for expr: %T", n)
 	}
 
-	typ := o.queryPkgInfo.TypeOf(expr)
-	constVal := o.queryPkgInfo.ValueOf(expr)
+	typ := qpos.info.TypeOf(expr)
+	constVal := qpos.info.ValueOf(expr)
 
 	// From this point on, we cannot fail with an error.
 	// Failure to run the pointer analysis will be reported later.
@@ -386,11 +386,11 @@ func describeValue(o *oracle, path []ast.Node) (*describeValueResult, error) {
 		var value ssa.Value
 		if obj != nil {
 			// def/ref of func/var/const object
-			value, ptaErr = ssaValueForIdent(o, obj, path)
+			value, ptaErr = ssaValueForIdent(o.prog, qpos.info, obj, path)
 		} else {
 			// any other expression
-			if o.queryPkgInfo.ValueOf(path[0].(ast.Expr)) == nil { // non-constant?
-				value, ptaErr = ssaValueForExpr(o, path)
+			if qpos.info.ValueOf(path[0].(ast.Expr)) == nil { // non-constant?
+				value, ptaErr = ssaValueForExpr(o.prog, qpos.info, path)
 			}
 		}
 		if value != nil {
@@ -404,6 +404,7 @@ func describeValue(o *oracle, path []ast.Node) (*describeValueResult, error) {
 	}
 
 	return &describeValueResult{
+		qpos:     qpos,
 		expr:     expr,
 		typ:      typ,
 		constVal: constVal,
@@ -414,7 +415,7 @@ func describeValue(o *oracle, path []ast.Node) (*describeValueResult, error) {
 }
 
 // describePointer runs the pointer analysis of the selected SSA value.
-func describePointer(o *oracle, v ssa.Value, indirect bool) (ptrs []pointerResult, err error) {
+func describePointer(o *Oracle, v ssa.Value, indirect bool) (ptrs []pointerResult, err error) {
 	buildSSA(o)
 
 	// TODO(adonovan): don't run indirect pointer analysis on non-ptr-ptrlike types.
@@ -454,6 +455,7 @@ type pointerResult struct {
 }
 
 type describeValueResult struct {
+	qpos     *QueryPos
 	expr     ast.Expr        // query node
 	typ      types.Type      // type of expression
 	constVal exact.Value     // value of expression, if constant
@@ -524,7 +526,7 @@ func (r *describeValueResult) display(printf printfFunc) {
 		// reflect.Value expression.
 
 		if len(r.ptrs) > 0 {
-			printf(false, "this %s may contain these dynamic types:", r.typ)
+			printf(r.qpos, "this %s may contain these dynamic types:", r.typ)
 			for _, ptr := range r.ptrs {
 				var obj types.Object
 				if nt, ok := deref(ptr.typ).(*types.Named); ok {
@@ -538,15 +540,15 @@ func (r *describeValueResult) display(printf printfFunc) {
 				}
 			}
 		} else {
-			printf(false, "this %s cannot contain any dynamic types.", r.typ)
+			printf(r.qpos, "this %s cannot contain any dynamic types.", r.typ)
 		}
 	} else {
 		// Show labels for other expressions.
 		if ptr := r.ptrs[0]; len(ptr.labels) > 0 {
-			printf(false, "value may point to these labels:")
+			printf(r.qpos, "value may point to these labels:")
 			printLabels(printf, ptr.labels, "\t")
 		} else {
-			printf(false, "value cannot point to anything.")
+			printf(r.qpos, "value cannot point to anything.")
 		}
 	}
 }
@@ -622,12 +624,12 @@ func printLabels(printf printfFunc, labels []*pointer.Label, prefix string) {
 
 // ---- TYPE ------------------------------------------------------------
 
-func describeType(o *oracle, path []ast.Node) (*describeTypeResult, error) {
+func describeType(o *Oracle, qpos *QueryPos, path []ast.Node) (*describeTypeResult, error) {
 	var description string
 	var t types.Type
 	switch n := path[0].(type) {
 	case *ast.Ident:
-		t = o.queryPkgInfo.TypeOf(n)
+		t = qpos.info.TypeOf(n)
 		switch t := t.(type) {
 		case *types.Basic:
 			description = "reference to built-in type " + t.String()
@@ -642,7 +644,7 @@ func describeType(o *oracle, path []ast.Node) (*describeTypeResult, error) {
 		}
 
 	case ast.Expr:
-		t = o.queryPkgInfo.TypeOf(n)
+		t = qpos.info.TypeOf(n)
 		description = "type " + t.String()
 
 	default:
@@ -654,7 +656,7 @@ func describeType(o *oracle, path []ast.Node) (*describeTypeResult, error) {
 		node:        path[0],
 		description: description,
 		typ:         t,
-		methods:     accessibleMethods(t, o.queryPkgInfo.Pkg),
+		methods:     accessibleMethods(t, qpos.info.Pkg),
 	}, nil
 }
 
@@ -708,7 +710,7 @@ func (r *describeTypeResult) toJSON(res *json.Result, fset *token.FileSet) {
 
 // ---- PACKAGE ------------------------------------------------------------
 
-func describePackage(o *oracle, path []ast.Node) (*describePackageResult, error) {
+func describePackage(o *Oracle, qpos *QueryPos, path []ast.Node) (*describePackageResult, error) {
 	var description string
 	var pkg *types.Package
 	switch n := path[0].(type) {
@@ -724,12 +726,12 @@ func describePackage(o *oracle, path []ast.Node) (*describePackageResult, error)
 	case *ast.Ident:
 		if _, isDef := path[1].(*ast.File); isDef {
 			// e.g. package id
-			pkg = o.queryPkgInfo.Pkg
+			pkg = qpos.info.Pkg
 			description = fmt.Sprintf("definition of package %q", pkg.Path())
 		} else {
 			// e.g. import id
 			//  or  id.F()
-			pkg = o.queryPkgInfo.ObjectOf(n).Pkg()
+			pkg = qpos.info.ObjectOf(n).Pkg()
 			description = fmt.Sprintf("reference to package %q", pkg.Path())
 		}
 
@@ -744,11 +746,11 @@ func describePackage(o *oracle, path []ast.Node) (*describePackageResult, error)
 		// Enumerate the accessible package members
 		// in lexicographic order.
 		for _, name := range pkg.Scope().Names() {
-			if pkg == o.queryPkgInfo.Pkg || ast.IsExported(name) {
+			if pkg == qpos.info.Pkg || ast.IsExported(name) {
 				mem := pkg.Scope().Lookup(name)
 				var methods []*types.Selection
 				if mem, ok := mem.(*types.TypeName); ok {
-					methods = accessibleMethods(mem.Type(), o.queryPkgInfo.Pkg)
+					methods = accessibleMethods(mem.Type(), qpos.info.Pkg)
 				}
 				members = append(members, &describeMember{
 					mem,
@@ -878,11 +880,11 @@ func tokenOf(o types.Object) string {
 
 // ---- STATEMENT ------------------------------------------------------------
 
-func describeStmt(o *oracle, path []ast.Node) (*describeStmtResult, error) {
+func describeStmt(o *Oracle, qpos *QueryPos, path []ast.Node) (*describeStmtResult, error) {
 	var description string
 	switch n := path[0].(type) {
 	case *ast.Ident:
-		if o.queryPkgInfo.ObjectOf(n).Pos() == n.Pos() {
+		if qpos.info.ObjectOf(n).Pos() == n.Pos() {
 			description = "labelled statement"
 		} else {
 			description = "reference to labelled statement"
diff --git a/oracle/freevars.go b/oracle/freevars.go
index 07973f2a..5e5d7548 100644
--- a/oracle/freevars.go
+++ b/oracle/freevars.go
@@ -26,9 +26,9 @@ import (
 // these might be interesting.  Perhaps group the results into three
 // bands.
 //
-func freevars(o *oracle) (queryResult, error) {
-	file := o.queryPath[len(o.queryPath)-1] // the enclosing file
-	fileScope := o.queryPkgInfo.Scopes[file]
+func freevars(o *Oracle, qpos *QueryPos) (queryResult, error) {
+	file := qpos.path[len(qpos.path)-1] // the enclosing file
+	fileScope := qpos.info.Scopes[file]
 	pkgScope := fileScope.Parent()
 
 	// The id and sel functions return non-nil if they denote an
@@ -49,7 +49,7 @@ func freevars(o *oracle) (queryResult, error) {
 	}
 
 	id = func(n *ast.Ident) types.Object {
-		obj := o.queryPkgInfo.ObjectOf(n)
+		obj := qpos.info.ObjectOf(n)
 		if obj == nil {
 			return nil // TODO(adonovan): fix: this fails for *types.Label.
 			panic(o.errorf(n, "no types.Object for ast.Ident"))
@@ -70,7 +70,7 @@ func freevars(o *oracle) (queryResult, error) {
 		if scope == fileScope || scope == pkgScope {
 			return nil // defined at file or package scope
 		}
-		if o.startPos <= obj.Pos() && obj.Pos() <= o.endPos {
+		if qpos.start <= obj.Pos() && obj.Pos() <= qpos.end {
 			return nil // defined within selection => not free
 		}
 		return obj
@@ -82,7 +82,7 @@ func freevars(o *oracle) (queryResult, error) {
 	refsMap := make(map[string]freevarsRef)
 
 	// Visit all the identifiers in the selected ASTs.
-	ast.Inspect(o.queryPath[0], func(n ast.Node) bool {
+	ast.Inspect(qpos.path[0], func(n ast.Node) bool {
 		if n == nil {
 			return true // popping DFS stack
 		}
@@ -90,7 +90,7 @@ func freevars(o *oracle) (queryResult, error) {
 		// Is this node contained within the selection?
 		// (freevars permits inexact selections,
 		// like two stmts in a block.)
-		if o.startPos <= n.Pos() && n.End() <= o.endPos {
+		if qpos.start <= n.Pos() && n.End() <= qpos.end {
 			var obj types.Object
 			var prune bool
 			switch n := n.(type) {
@@ -119,7 +119,7 @@ func freevars(o *oracle) (queryResult, error) {
 					panic(obj)
 				}
 
-				typ := o.queryPkgInfo.TypeOf(n.(ast.Expr))
+				typ := qpos.info.TypeOf(n.(ast.Expr))
 				ref := freevarsRef{kind, o.printNode(n), typ, obj}
 				refsMap[ref.ref] = ref
 
@@ -139,12 +139,14 @@ func freevars(o *oracle) (queryResult, error) {
 	sort.Sort(byRef(refs))
 
 	return &freevarsResult{
+		qpos: qpos,
 		fset: o.prog.Fset,
 		refs: refs,
 	}, nil
 }
 
 type freevarsResult struct {
+	qpos *QueryPos
 	fset *token.FileSet
 	refs []freevarsRef
 }
@@ -158,9 +160,9 @@ type freevarsRef struct {
 
 func (r *freevarsResult) display(printf printfFunc) {
 	if len(r.refs) == 0 {
-		printf(false, "No free identifers.")
+		printf(r.qpos, "No free identifiers.")
 	} else {
-		printf(false, "Free identifers:")
+		printf(r.qpos, "Free identifiers:")
 		for _, ref := range r.refs {
 			printf(ref.obj, "%s %s %s", ref.kind, ref.ref, ref.typ)
 		}
diff --git a/oracle/implements.go b/oracle/implements.go
index b31617a2..d26cd1ec 100644
--- a/oracle/implements.go
+++ b/oracle/implements.go
@@ -30,8 +30,8 @@ import (
 //   actually occur, with examples?  (NB: this is not a conservative
 //   answer due to ChangeInterface, i.e. subtyping among interfaces.)
 //
-func implements(o *oracle) (queryResult, error) {
-	pkg := o.queryPkgInfo.Pkg
+func implements(o *Oracle, qpos *QueryPos) (queryResult, error) {
+	pkg := qpos.info.Pkg
 
 	// Compute set of named interface/concrete types at package level.
 	var interfaces, concretes []*types.Named
diff --git a/oracle/oracle.go b/oracle/oracle.go
index e462ed54..b53095cc 100644
--- a/oracle/oracle.go
+++ b/oracle/oracle.go
@@ -2,6 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Package oracle contains the implementation of the oracle tool whose
+// command-line is provided by code.google.com/p/go.tools/cmd/oracle.
+//
+// http://golang.org/s/oracle-design
+// http://golang.org/s/oracle-user-manual
+//
 package oracle
 
 // This file defines oracle.Query, the entry point for the oracle tool.
@@ -33,16 +39,12 @@ import (
 	"code.google.com/p/go.tools/ssa"
 )
 
-type oracle struct {
+// An Oracle holds the program state required for one or more queries.
+type Oracle struct {
 	out    io.Writer      // standard output
 	prog   *ssa.Program   // the SSA program [only populated if need&SSA]
 	config pointer.Config // pointer analysis configuration
 
-	// need&(Pos|ExactPos):
-	startPos, endPos token.Pos             // source extent of query
-	queryPkgInfo     *importer.PackageInfo // type info for the queried package
-	queryPath        []ast.Node            // AST path from query node to root of ast.File
-
 	// need&AllTypeInfo
 	typeInfo map[*types.Package]*importer.PackageInfo // type info for all ASTs in the program
 
@@ -53,30 +55,42 @@ type oracle struct {
 //
 // Typed ASTs for the whole program are always constructed
 // transiently; they are retained only for the queried package unless
-// AllTypeInfo is set.
+// needAllTypeInfo is set.
 const (
-	Pos         = 1 << iota // needs a position
-	ExactPos                // needs an exact AST selection; implies Pos
-	AllTypeInfo             // needs to retain type info for all ASTs in the program
-	SSA                     // needs ssa.Packages for whole program
-	PTA         = SSA       // needs pointer analysis
+	needPos         = 1 << iota // needs a position
+	needExactPos                // needs an exact AST selection; implies needPos
+	needAllTypeInfo             // needs to retain type info for all ASTs in the program
+	needSSA                     // needs ssa.Packages for whole program
+	needSSADebug                // needs debug info for ssa.Packages
+	needPTA         = needSSA   // needs pointer analysis
+	needAll         = -1        // needs everything (e.g. a sequence of queries)
 )
 
 type modeInfo struct {
+	name  string
 	needs int
-	impl  func(*oracle) (queryResult, error)
+	impl  func(*Oracle, *QueryPos) (queryResult, error)
 }
 
-var modes = map[string]modeInfo{
-	"callees":    modeInfo{PTA | ExactPos, callees},
-	"callers":    modeInfo{PTA | Pos, callers},
-	"callgraph":  modeInfo{PTA, callgraph},
-	"callstack":  modeInfo{PTA | Pos, callstack},
-	"describe":   modeInfo{PTA | ExactPos, describe},
-	"freevars":   modeInfo{Pos, freevars},
-	"implements": modeInfo{Pos, implements},
-	"peers":      modeInfo{PTA | Pos, peers},
-	"referrers":  modeInfo{AllTypeInfo | Pos, referrers},
+var modes = []*modeInfo{
+	{"callees", needPTA | needExactPos, callees},
+	{"callers", needPTA | needPos, callers},
+	{"callgraph", needPTA, callgraph},
+	{"callstack", needPTA | needPos, callstack},
+	{"describe", needPTA | needSSADebug | needExactPos, describe},
+	{"freevars", needPos, freevars},
+	{"implements", needPos, implements},
+	{"peers", needPTA | needSSADebug | needPos, peers},
+	{"referrers", needAllTypeInfo | needPos, referrers},
+}
+
+func findMode(mode string) *modeInfo {
+	for _, m := range modes {
+		if m.name == mode {
+			return m
+		}
+	}
+	return nil
 }
 
 type printfFunc func(pos interface{}, format string, args ...interface{})
@@ -93,6 +107,17 @@ type warning struct {
 	args   []interface{}
 }
 
+// A QueryPos represents the position provided as input to a query:
+// a textual extent in the program's source code, the AST node it
+// corresponds to, and the package to which it belongs.
+// Instances are created by ParseQueryPos.
+//
+type QueryPos struct {
+	start, end token.Pos             // source extent of query
+	info       *importer.PackageInfo // type info for the queried package
+	path       []ast.Node            // AST path from query node to root of ast.File
+}
+
 // A Result encapsulates the result of an oracle.Query.
 //
 // Result instances implement the json.Marshaler interface, i.e. they
@@ -118,41 +143,91 @@ func (res *Result) MarshalJSON() ([]byte, error) {
 	return encjson.Marshal(resj)
 }
 
-// Query runs the oracle.
+// Query runs a single oracle query.
+//
 // args specify the main package in importer.CreatePackageFromArgs syntax.
 // mode is the query mode ("callers", etc).
-// pos is the selection in parseQueryPos() syntax.
 // ptalog is the (optional) pointer-analysis log file.
-// buildContext is the optional configuration for locating packages.
+// buildContext is the go/build configuration for locating packages.
+//
+// Clients that intend to perform multiple queries against the same
+// analysis scope should use this pattern instead:
+//
+//	imp := importer.New(&importer.Config{Build: buildContext})
+// 	o, err := oracle.New(imp, args, nil)
+//	if err != nil { ... }
+//	for ... {
+//		qpos, err := oracle.ParseQueryPos(imp, pos, needExact)
+//		if err != nil { ... }
+//
+//		res, err := o.Query(mode, qpos)
+//		if err != nil { ... }
+//
+//		// use res
+//	}
+//
+// TODO(adonovan): the ideal 'needsExact' parameter for ParseQueryPos
+// depends on the query mode; how should we expose this?
 //
 func Query(args []string, mode, pos string, ptalog io.Writer, buildContext *build.Context) (*Result, error) {
-	minfo, ok := modes[mode]
-	if !ok {
+	minfo := findMode(mode)
+	if minfo == nil {
 		return nil, fmt.Errorf("invalid mode type: %q", mode)
 	}
 
 	imp := importer.New(&importer.Config{Build: buildContext})
-	o := &oracle{
+	o, err := New(imp, args, ptalog)
+	if err != nil {
+		return nil, err
+	}
+
+	// Phase timing diagnostics.
+	// TODO(adonovan): needs more work.
+	// if false {
+	// 	defer func() {
+	// 		fmt.Println()
+	// 		for name, duration := range o.timers {
+	// 			fmt.Printf("# %-30s %s\n", name, duration)
+	// 		}
+	// 	}()
+	// }
+
+	var qpos *QueryPos
+	if minfo.needs&(needPos|needExactPos) != 0 {
+		var err error
+		qpos, err = ParseQueryPos(imp, pos, minfo.needs&needExactPos != 0)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// SSA is built and we have the QueryPos.
+	// Release the other ASTs and type info to the GC.
+	imp = nil
+
+	return o.query(minfo, qpos)
+}
+
+// New constructs a new Oracle that can be used for a sequence of queries.
+//
+// imp will be used to load source code for imported packages.
+// It must not yet have loaded any packages.
+//
+// args specify the main package in importer.CreatePackageFromArgs syntax.
+//
+// ptalog is the (optional) pointer-analysis log file.
+//
+func New(imp *importer.Importer, args []string, ptalog io.Writer) (*Oracle, error) {
+	return newOracle(imp, args, ptalog, needAll)
+}
+
+func newOracle(imp *importer.Importer, args []string, ptalog io.Writer, needs int) (*Oracle, error) {
+	o := &Oracle{
 		prog:   ssa.NewProgram(imp.Fset, 0),
 		timers: make(map[string]time.Duration),
 	}
 	o.config.Log = ptalog
 
-	var res Result
-	o.config.Warn = func(pos token.Pos, format string, args ...interface{}) {
-		res.warnings = append(res.warnings, warning{pos, format, args})
-	}
-
-	// Phase timing diagnostics.
-	if false {
-		defer func() {
-			fmt.Println()
-			for name, duration := range o.timers {
-				fmt.Printf("# %-30s %s\n", name, duration)
-			}
-		}()
-	}
-
 	// Load/parse/type-check program from args.
 	start := time.Now()
 	initialPkgInfos, args, err := imp.LoadInitialPackages(args)
@@ -165,7 +240,7 @@ func Query(args []string, mode, pos string, ptalog io.Writer, buildContext *buil
 	o.timers["load/parse/type"] = time.Since(start)
 
 	// Retain type info for all ASTs in the program.
-	if minfo.needs&AllTypeInfo != 0 {
+	if needs&needAllTypeInfo != 0 {
 		m := make(map[*types.Package]*importer.PackageInfo)
 		for _, p := range imp.AllPackages() {
 			m[p.Pkg] = p
@@ -173,32 +248,13 @@ func Query(args []string, mode, pos string, ptalog io.Writer, buildContext *buil
 		o.typeInfo = m
 	}
 
-	// Parse the source query position.
-	if minfo.needs&(Pos|ExactPos) != 0 {
-		var err error
-		o.startPos, o.endPos, err = parseQueryPos(o.prog.Fset, pos)
-		if err != nil {
-			return nil, err
-		}
-
-		var exact bool
-		o.queryPkgInfo, o.queryPath, exact = imp.PathEnclosingInterval(o.startPos, o.endPos)
-		if o.queryPath == nil {
-			return nil, o.errorf(false, "no syntax here")
-		}
-		if minfo.needs&ExactPos != 0 && !exact {
-			return nil, o.errorf(o.queryPath[0], "ambiguous selection within %s",
-				importer.NodeDescription(o.queryPath[0]))
-		}
-	}
-
 	// Create SSA package for the initial package and its dependencies.
-	if minfo.needs&SSA != 0 {
+	if needs&needSSA != 0 {
 		start = time.Now()
 
 		// Create SSA packages.
 		if err := o.prog.CreatePackages(imp); err != nil {
-			return nil, o.errorf(false, "%s", err)
+			return nil, o.errorf(nil, "%s", err)
 		}
 
 		// Initial packages (specified on command line)
@@ -211,34 +267,66 @@ func Query(args []string, mode, pos string, ptalog io.Writer, buildContext *buil
 				// should build a single synthetic testmain package,
 				// not synthetic main functions to many packages.
 				if initialPkg.CreateTestMainFunction() == nil {
-					return nil, o.errorf(false, "analysis scope has no main() entry points")
+					return nil, o.errorf(nil, "analysis scope has no main() entry points")
 				}
 			}
 			o.config.Mains = append(o.config.Mains, initialPkg)
 		}
 
-		// Query package.
-		if o.queryPkgInfo != nil {
-			pkg := o.prog.Package(o.queryPkgInfo.Pkg)
-			pkg.SetDebugMode(true)
-			pkg.Build()
+		if needs&needSSADebug != 0 {
+			for _, pkg := range o.prog.AllPackages() {
+				pkg.SetDebugMode(true)
+			}
 		}
 
 		o.timers["SSA-create"] = time.Since(start)
 	}
 
-	// SSA is built and we have query{Path,PkgInfo}.
-	// Release the other ASTs and type info to the GC.
-	imp = nil
+	return o, nil
+}
 
-	res.q, err = minfo.impl(o)
+// Query runs the query of the specified mode and selection.
+func (o *Oracle) Query(mode string, qpos *QueryPos) (*Result, error) {
+	minfo := findMode(mode)
+	if minfo == nil {
+		return nil, fmt.Errorf("invalid mode type: %q", mode)
+	}
+	return o.query(minfo, qpos)
+}
+
+func (o *Oracle) query(minfo *modeInfo, qpos *QueryPos) (*Result, error) {
+	res := &Result{
+		mode:    minfo.name,
+		fset:    o.prog.Fset,
+		fprintf: o.fprintf, // captures o.prog, o.{start,end}Pos for later printing
+	}
+	o.config.Warn = func(pos token.Pos, format string, args ...interface{}) {
+		res.warnings = append(res.warnings, warning{pos, format, args})
+	}
+	var err error
+	res.q, err = minfo.impl(o, qpos)
 	if err != nil {
 		return nil, err
 	}
-	res.mode = mode
-	res.fset = o.prog.Fset
-	res.fprintf = o.fprintf // captures o.prog, o.{start,end}Pos for later printing
-	return &res, nil
+	return res, nil
+}
+
+// ParseQueryPos parses the source query position pos.
+// If needExact, it must identify a single AST subtree.
+//
+func ParseQueryPos(imp *importer.Importer, pos string, needExact bool) (*QueryPos, error) {
+	start, end, err := parseQueryPos(imp.Fset, pos)
+	if err != nil {
+		return nil, err
+	}
+	info, path, exact := imp.PathEnclosingInterval(start, end)
+	if path == nil {
+		return nil, errors.New("no syntax here")
+	}
+	if needExact && !exact {
+		return nil, fmt.Errorf("ambiguous selection within %s", importer.NodeDescription(path[0]))
+	}
+	return &QueryPos{start, end, info, path}, nil
 }
 
 // WriteTo writes the oracle query result res to out in a compiler diagnostic format.
@@ -262,7 +350,7 @@ func (res *Result) WriteTo(out io.Writer) {
 // buildSSA constructs the SSA representation of Go-source function bodies.
 // Not needed in simpler modes, e.g. freevars.
 //
-func buildSSA(o *oracle) {
+func buildSSA(o *Oracle) {
 	start := time.Now()
 	o.prog.BuildAll()
 	o.timers["SSA-build"] = time.Since(start)
@@ -271,7 +359,7 @@ func buildSSA(o *oracle) {
 // ptrAnalysis runs the pointer analysis and returns the synthetic
 // root of the callgraph.
 //
-func ptrAnalysis(o *oracle) pointer.CallGraphNode {
+func ptrAnalysis(o *Oracle) pointer.CallGraphNode {
 	start := time.Now()
 	root := pointer.Analyze(&o.config)
 	o.timers["pointer analysis"] = time.Since(start)
@@ -399,15 +487,14 @@ func deref(typ types.Type) types.Type {
 //    - an ast.Node, denoting an interval
 //    - anything with a Pos() method:
 //         ssa.Member, ssa.Value, ssa.Instruction, types.Object, pointer.Label, etc.
-//    - a bool, meaning the extent [o.startPos, o.endPos) of the user's query.
-//      (the value is ignored)
+//    - a QueryPos, denoting the extent of the user's query.
 //    - nil, meaning no position at all.
 //
 // The output format is is compatible with the 'gnu'
 // compilation-error-regexp in Emacs' compilation mode.
 // TODO(adonovan): support other editors.
 //
-func (o *oracle) fprintf(w io.Writer, pos interface{}, format string, args ...interface{}) {
+func (o *Oracle) fprintf(w io.Writer, pos interface{}, format string, args ...interface{}) {
 	var start, end token.Pos
 	switch pos := pos.(type) {
 	case ast.Node:
@@ -421,9 +508,9 @@ func (o *oracle) fprintf(w io.Writer, pos interface{}, format string, args ...in
 	}:
 		start = pos.Pos()
 		end = start
-	case bool:
-		start = o.startPos
-		end = o.endPos
+	case *QueryPos:
+		start = pos.start
+		end = pos.end
 	case nil:
 		// no-op
 	default:
@@ -448,14 +535,14 @@ func (o *oracle) fprintf(w io.Writer, pos interface{}, format string, args ...in
 }
 
 // errorf is like fprintf, but returns a formatted error string.
-func (o *oracle) errorf(pos interface{}, format string, args ...interface{}) error {
+func (o *Oracle) errorf(pos interface{}, format string, args ...interface{}) error {
 	var buf bytes.Buffer
 	o.fprintf(&buf, pos, format, args...)
 	return errors.New(buf.String())
 }
 
 // printNode returns the pretty-printed syntax of n.
-func (o *oracle) printNode(n ast.Node) string {
+func (o *Oracle) printNode(n ast.Node) string {
 	var buf bytes.Buffer
 	printer.Fprint(&buf, o.prog.Fset, n)
 	return buf.String()
diff --git a/oracle/oracle_test.go b/oracle/oracle_test.go
index 12b9c687..097ecf4c 100644
--- a/oracle/oracle_test.go
+++ b/oracle/oracle_test.go
@@ -44,6 +44,7 @@ import (
 	"strings"
 	"testing"
 
+	"code.google.com/p/go.tools/importer"
 	"code.google.com/p/go.tools/oracle"
 )
 
@@ -249,3 +250,53 @@ func TestOracle(t *testing.T) {
 		}
 	}
 }
+
+func TestMultipleQueries(t *testing.T) {
+	// Importer
+	var buildContext = build.Default
+	buildContext.GOPATH = "testdata"
+	imp := importer.New(&importer.Config{Build: &buildContext})
+
+	// Oracle
+	filename := "testdata/src/main/multi.go"
+	o, err := oracle.New(imp, []string{filename}, nil)
+	if err != nil {
+		t.Fatalf("oracle.New failed: %s", err)
+	}
+
+	// QueryPos
+	pos := filename + ":#54,#58"
+	qpos, err := oracle.ParseQueryPos(imp, pos, true)
+	if err != nil {
+		t.Fatalf("oracle.ParseQueryPos(%q) failed: %s", pos, err)
+	}
+	// SSA is built and we have the QueryPos.
+	// Release the other ASTs and type info to the GC.
+	imp = nil
+
+	// Run different query moes on same scope and selection.
+	out := new(bytes.Buffer)
+	for _, mode := range [...]string{"callers", "describe", "freevars"} {
+		res, err := o.Query(mode, qpos)
+		if err != nil {
+			t.Errorf("(*oracle.Oracle).Query(%q) failed: %s", pos, err)
+		}
+		capture := new(bytes.Buffer) // capture standard output
+		res.WriteTo(capture)
+		for _, line := range strings.Split(capture.String(), "\n") {
+			fmt.Fprintf(out, "%s\n", stripLocation(line))
+		}
+	}
+	want := `multi.f is called from these 1 sites:
+	static function call from multi.main
+
+function call (or conversion) of type ()
+
+Free identifiers:
+var x int
+
+`
+	if got := out.String(); got != want {
+		t.Errorf("Query output differs; want <<%s>>, got <<%s>>\n", want, got)
+	}
+}
diff --git a/oracle/peers.go b/oracle/peers.go
index 23dd1bef..09dba85d 100644
--- a/oracle/peers.go
+++ b/oracle/peers.go
@@ -22,10 +22,10 @@ import (
 // TODO(adonovan): permit the user to query based on a MakeChan (not send/recv),
 // or the implicit receive in "for v := range ch".
 //
-func peers(o *oracle) (queryResult, error) {
-	arrowPos := findArrow(o)
+func peers(o *Oracle, qpos *QueryPos) (queryResult, error) {
+	arrowPos := findArrow(qpos)
 	if arrowPos == token.NoPos {
-		return nil, o.errorf(o.queryPath[0], "there is no send/receive here")
+		return nil, o.errorf(qpos.path[0], "there is no send/receive here")
 	}
 
 	buildSSA(o)
@@ -111,8 +111,8 @@ func peers(o *oracle) (queryResult, error) {
 // findArrow returns the position of the enclosing send/receive op
 // (<-) for the query position, or token.NoPos if not found.
 //
-func findArrow(o *oracle) token.Pos {
-	for _, n := range o.queryPath {
+func findArrow(qpos *QueryPos) token.Pos {
+	for _, n := range qpos.path {
 		switch n := n.(type) {
 		case *ast.UnaryExpr:
 			if n.Op == token.ARROW {
diff --git a/oracle/referrers.go b/oracle/referrers.go
index ab369d07..4bf16bd8 100644
--- a/oracle/referrers.go
+++ b/oracle/referrers.go
@@ -16,16 +16,16 @@ import (
 // Referrers reports all identifiers that resolve to the same object
 // as the queried identifier, within any package in the analysis scope.
 //
-func referrers(o *oracle) (queryResult, error) {
-	id, _ := o.queryPath[0].(*ast.Ident)
+func referrers(o *Oracle, qpos *QueryPos) (queryResult, error) {
+	id, _ := qpos.path[0].(*ast.Ident)
 	if id == nil {
-		return nil, o.errorf(false, "no identifier here")
+		return nil, o.errorf(qpos, "no identifier here")
 	}
 
-	obj := o.queryPkgInfo.ObjectOf(id)
+	obj := qpos.info.ObjectOf(id)
 	if obj == nil {
 		// Happens for y in "switch y := x.(type)", but I think that's all.
-		return nil, o.errorf(false, "no object for identifier")
+		return nil, o.errorf(qpos, "no object for identifier")
 	}
 
 	// Iterate over all go/types' resolver facts for the entire program.
diff --git a/oracle/testdata/src/main/calls.golden b/oracle/testdata/src/main/calls.golden
index e0312884..225570a7 100644
--- a/oracle/testdata/src/main/calls.golden
+++ b/oracle/testdata/src/main/calls.golden
@@ -80,7 +80,6 @@ Error: this is a type conversion, not a function call
 -------- @callees callees-err-bad-selection --------
 
 Error: ambiguous selection within function call (or conversion)
-
 -------- @callees callees-err-deadcode1 --------
 
 Error: this call site is unreachable in this analysis
diff --git a/oracle/testdata/src/main/freevars.golden b/oracle/testdata/src/main/freevars.golden
index 4b29fa45..a4c2c77c 100644
--- a/oracle/testdata/src/main/freevars.golden
+++ b/oracle/testdata/src/main/freevars.golden
@@ -1,11 +1,11 @@
 -------- @freevars fv1 --------
-Free identifers:
+Free identifiers:
 type C main.C
 const exp int
 var x int
 
 -------- @freevars fv2 --------
-Free identifers:
+Free identifiers:
 var s.t.a int
 var s.t.b int
 var s.x int
@@ -13,6 +13,6 @@ var x int
 var y int32
 
 -------- @freevars fv3 --------
-Free identifers:
+Free identifiers:
 var x int
 
diff --git a/oracle/testdata/src/main/multi.go b/oracle/testdata/src/main/multi.go
new file mode 100644
index 00000000..54caf15d
--- /dev/null
+++ b/oracle/testdata/src/main/multi.go
@@ -0,0 +1,13 @@
+package multi
+
+func g(x int) {
+}
+
+func f() {
+	x := 1
+	g(x) // "g(x)" is the selection for multiple queries
+}
+
+func main() {
+	f()
+}