diff --git a/cmd/oracle/main.go b/cmd/oracle/main.go
index 05f33d05..5dff0547 100644
--- a/cmd/oracle/main.go
+++ b/cmd/oracle/main.go
@@ -14,8 +14,8 @@ package main
 
 import (
 	"bufio"
-	"bytes"
 	"encoding/json"
+	"encoding/xml"
 	"flag"
 	"fmt"
 	"go/build"
@@ -39,7 +39,7 @@ var modeFlag = flag.String("mode", "",
 var ptalogFlag = flag.String("ptalog", "",
 	"Location of the points-to analysis log file, or empty to disable logging.")
 
-var formatFlag = flag.String("format", "plain", "Output format: 'plain' or 'json'.")
+var formatFlag = flag.String("format", "plain", "Output format.  One of {plain,json,xml}.")
 
 // TODO(adonovan): eliminate or flip this flag after PTA presolver is implemented.
 var reflectFlag = flag.Bool("reflect", true, "Analyze reflection soundly (slow).")
@@ -53,6 +53,7 @@ The -format flag controls the output format:
 	plain	an editor-friendly format in which every line of output
 		is of the form "pos: text", where pos is "-" if unknown.
 	json	structured data in JSON syntax.
+	xml	structured data in XML syntax.
 
 The -pos flag is required in all modes except 'callgraph'.
 
@@ -140,7 +141,10 @@ func main() {
 	}
 
 	// -format flag
-	if *formatFlag != "json" && *formatFlag != "plain" {
+	switch *formatFlag {
+	case "json", "plain", "xml":
+		// ok
+	default:
 		fmt.Fprintf(os.Stderr, "Error: illegal -format value: %q\n"+useHelp, *formatFlag)
 		os.Exit(2)
 	}
@@ -161,17 +165,20 @@ func main() {
 	// Print the result.
 	switch *formatFlag {
 	case "json":
-		b, err := json.Marshal(res)
+		b, err := json.MarshalIndent(res.Serial(), "", "\t")
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "JSON error: %s\n", err)
 			os.Exit(1)
 		}
-		var buf bytes.Buffer
-		if err := json.Indent(&buf, b, "", "\t"); err != nil {
-			fmt.Fprintf(os.Stderr, "json.Indent failed: %s", err)
+		os.Stdout.Write(b)
+
+	case "xml":
+		b, err := xml.MarshalIndent(res.Serial(), "", "\t")
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "XML error: %s\n", err)
 			os.Exit(1)
 		}
-		os.Stdout.Write(buf.Bytes())
+		os.Stdout.Write(b)
 
 	case "plain":
 		res.WriteTo(os.Stdout)
diff --git a/oracle/callees.go b/oracle/callees.go
index a9ee1890..66a10c37 100644
--- a/oracle/callees.go
+++ b/oracle/callees.go
@@ -10,7 +10,7 @@ import (
 	"sort"
 
 	"code.google.com/p/go.tools/go/types"
-	"code.google.com/p/go.tools/oracle/json"
+	"code.google.com/p/go.tools/oracle/serial"
 	"code.google.com/p/go.tools/pointer"
 	"code.google.com/p/go.tools/ssa"
 )
@@ -113,13 +113,13 @@ func (r *calleesResult) display(printf printfFunc) {
 	}
 }
 
-func (r *calleesResult) toJSON(res *json.Result, fset *token.FileSet) {
-	j := &json.Callees{
+func (r *calleesResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	j := &serial.Callees{
 		Pos:  fset.Position(r.site.Pos()).String(),
 		Desc: r.site.Description(),
 	}
 	for _, callee := range r.funcs {
-		j.Callees = append(j.Callees, &json.CalleesItem{
+		j.Callees = append(j.Callees, &serial.CalleesItem{
 			Name: callee.String(),
 			Pos:  fset.Position(callee.Pos()).String(),
 		})
diff --git a/oracle/callers.go b/oracle/callers.go
index 01f827be..1233bccd 100644
--- a/oracle/callers.go
+++ b/oracle/callers.go
@@ -7,7 +7,7 @@ package oracle
 import (
 	"go/token"
 
-	"code.google.com/p/go.tools/oracle/json"
+	"code.google.com/p/go.tools/oracle/serial"
 	"code.google.com/p/go.tools/pointer"
 	"code.google.com/p/go.tools/ssa"
 )
@@ -73,10 +73,10 @@ func (r *callersResult) display(printf printfFunc) {
 	}
 }
 
-func (r *callersResult) toJSON(res *json.Result, fset *token.FileSet) {
-	var callers []json.Caller
+func (r *callersResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	var callers []serial.Caller
 	for _, site := range r.calls {
-		var c json.Caller
+		var c serial.Caller
 		c.Caller = site.Caller().Func().String()
 		if site.Caller() == r.root {
 			c.Desc = "synthetic call"
diff --git a/oracle/callgraph.go b/oracle/callgraph.go
index c8cdd680..3598fd84 100644
--- a/oracle/callgraph.go
+++ b/oracle/callgraph.go
@@ -8,7 +8,7 @@ import (
 	"go/token"
 	"strings"
 
-	"code.google.com/p/go.tools/oracle/json"
+	"code.google.com/p/go.tools/oracle/serial"
 	"code.google.com/p/go.tools/pointer"
 )
 
@@ -90,8 +90,8 @@ Some nodes may appear multiple times due to context-sensitive
 	print(r.root, 0)
 }
 
-func (r *callgraphResult) toJSON(res *json.Result, fset *token.FileSet) {
-	cg := make([]json.CallGraph, len(r.numbering))
+func (r *callgraphResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	cg := make([]serial.CallGraph, len(r.numbering))
 	for n, i := range r.numbering {
 		j := &cg[i]
 		fn := n.Func()
diff --git a/oracle/callstack.go b/oracle/callstack.go
index 6a5f4323..afec7554 100644
--- a/oracle/callstack.go
+++ b/oracle/callstack.go
@@ -7,7 +7,7 @@ package oracle
 import (
 	"go/token"
 
-	"code.google.com/p/go.tools/oracle/json"
+	"code.google.com/p/go.tools/oracle/serial"
 	"code.google.com/p/go.tools/pointer"
 	"code.google.com/p/go.tools/ssa"
 )
@@ -98,16 +98,16 @@ func (r *callstackResult) display(printf printfFunc) {
 	}
 }
 
-func (r *callstackResult) toJSON(res *json.Result, fset *token.FileSet) {
-	var callers []json.Caller
+func (r *callstackResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	var callers []serial.Caller
 	for _, site := range r.callstack {
-		callers = append(callers, json.Caller{
+		callers = append(callers, serial.Caller{
 			Pos:    fset.Position(site.Pos()).String(),
 			Caller: site.Caller().Func().String(),
 			Desc:   site.Description(),
 		})
 	}
-	res.Callstack = &json.CallStack{
+	res.Callstack = &serial.CallStack{
 		Pos:     fset.Position(r.target.Pos()).String(),
 		Target:  r.target.String(),
 		Callers: callers,
diff --git a/oracle/describe.go b/oracle/describe.go
index 2c30823c..688beeb4 100644
--- a/oracle/describe.go
+++ b/oracle/describe.go
@@ -17,7 +17,7 @@ import (
 	"code.google.com/p/go.tools/go/exact"
 	"code.google.com/p/go.tools/go/types"
 	"code.google.com/p/go.tools/importer"
-	"code.google.com/p/go.tools/oracle/json"
+	"code.google.com/p/go.tools/oracle/serial"
 	"code.google.com/p/go.tools/pointer"
 	"code.google.com/p/go.tools/ssa"
 )
@@ -70,8 +70,8 @@ func (r *describeUnknownResult) display(printf printfFunc) {
 	printf(r.node, "%s", importer.NodeDescription(r.node))
 }
 
-func (r *describeUnknownResult) toJSON(res *json.Result, fset *token.FileSet) {
-	res.Describe = &json.Describe{
+func (r *describeUnknownResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	res.Describe = &serial.Describe{
 		Desc: importer.NodeDescription(r.node),
 		Pos:  fset.Position(r.node.Pos()).String(),
 	}
@@ -553,7 +553,7 @@ func (r *describeValueResult) display(printf printfFunc) {
 	}
 }
 
-func (r *describeValueResult) toJSON(res *json.Result, fset *token.FileSet) {
+func (r *describeValueResult) toSerial(res *serial.Result, fset *token.FileSet) {
 	var value, objpos, ptaerr string
 	if r.constVal != nil {
 		value = r.constVal.String()
@@ -565,31 +565,31 @@ func (r *describeValueResult) toJSON(res *json.Result, fset *token.FileSet) {
 		ptaerr = r.ptaErr.Error()
 	}
 
-	var pts []*json.DescribePointer
+	var pts []*serial.DescribePointer
 	for _, ptr := range r.ptrs {
 		var namePos string
 		if nt, ok := deref(ptr.typ).(*types.Named); ok {
 			namePos = fset.Position(nt.Obj().Pos()).String()
 		}
-		var labels []json.DescribePTALabel
+		var labels []serial.DescribePTALabel
 		for _, l := range ptr.labels {
-			labels = append(labels, json.DescribePTALabel{
+			labels = append(labels, serial.DescribePTALabel{
 				Pos:  fset.Position(l.Pos()).String(),
 				Desc: l.String(),
 			})
 		}
-		pts = append(pts, &json.DescribePointer{
+		pts = append(pts, &serial.DescribePointer{
 			Type:    ptr.typ.String(),
 			NamePos: namePos,
 			Labels:  labels,
 		})
 	}
 
-	res.Describe = &json.Describe{
+	res.Describe = &serial.Describe{
 		Desc:   importer.NodeDescription(r.expr),
 		Pos:    fset.Position(r.expr.Pos()).String(),
 		Detail: "value",
-		Value: &json.DescribeValue{
+		Value: &serial.DescribeValue{
 			Type:   r.typ.String(),
 			Value:  value,
 			ObjPos: objpos,
@@ -689,21 +689,21 @@ func (r *describeTypeResult) display(printf printfFunc) {
 	}
 }
 
-func (r *describeTypeResult) toJSON(res *json.Result, fset *token.FileSet) {
+func (r *describeTypeResult) toSerial(res *serial.Result, fset *token.FileSet) {
 	var namePos, nameDef string
 	if nt, ok := r.typ.(*types.Named); ok {
 		namePos = fset.Position(nt.Obj().Pos()).String()
 		nameDef = nt.Underlying().String()
 	}
-	res.Describe = &json.Describe{
+	res.Describe = &serial.Describe{
 		Desc:   r.description,
 		Pos:    fset.Position(r.node.Pos()).String(),
 		Detail: "type",
-		Type: &json.DescribeType{
+		Type: &serial.DescribeType{
 			Type:    r.typ.String(),
 			NamePos: namePos,
 			NameDef: nameDef,
-			Methods: methodsToJSON(r.methods, fset),
+			Methods: methodsToSerial(r.methods, fset),
 		},
 	}
 }
@@ -831,8 +831,8 @@ func formatMember(obj types.Object, maxname int) string {
 	return buf.String()
 }
 
-func (r *describePackageResult) toJSON(res *json.Result, fset *token.FileSet) {
-	var members []*json.DescribeMember
+func (r *describePackageResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	var members []*serial.DescribeMember
 	for _, mem := range r.members {
 		typ := mem.obj.Type()
 		var val string
@@ -842,20 +842,20 @@ func (r *describePackageResult) toJSON(res *json.Result, fset *token.FileSet) {
 		case *types.TypeName:
 			typ = typ.Underlying()
 		}
-		members = append(members, &json.DescribeMember{
+		members = append(members, &serial.DescribeMember{
 			Name:    mem.obj.Name(),
 			Type:    typ.String(),
 			Value:   val,
 			Pos:     fset.Position(mem.obj.Pos()).String(),
 			Kind:    tokenOf(mem.obj),
-			Methods: methodsToJSON(mem.methods, fset),
+			Methods: methodsToSerial(mem.methods, fset),
 		})
 	}
-	res.Describe = &json.Describe{
+	res.Describe = &serial.Describe{
 		Desc:   r.description,
 		Pos:    fset.Position(r.node.Pos()).String(),
 		Detail: "package",
-		Package: &json.DescribePackage{
+		Package: &serial.DescribePackage{
 			Path:    r.pkg.Path(),
 			Members: members,
 		},
@@ -907,8 +907,8 @@ func (r *describeStmtResult) display(printf printfFunc) {
 	printf(r.node, "%s", r.description)
 }
 
-func (r *describeStmtResult) toJSON(res *json.Result, fset *token.FileSet) {
-	res.Describe = &json.Describe{
+func (r *describeStmtResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	res.Describe = &serial.Describe{
 		Desc:   r.description,
 		Pos:    fset.Position(r.node.Pos()).String(),
 		Detail: "unknown",
@@ -946,10 +946,10 @@ func isAccessibleFrom(obj types.Object, pkg *types.Package) bool {
 	return ast.IsExported(obj.Name()) || obj.Pkg() == pkg
 }
 
-func methodsToJSON(methods []*types.Selection, fset *token.FileSet) []json.DescribeMethod {
-	var jmethods []json.DescribeMethod
+func methodsToSerial(methods []*types.Selection, fset *token.FileSet) []serial.DescribeMethod {
+	var jmethods []serial.DescribeMethod
 	for _, meth := range methods {
-		jmethods = append(jmethods, json.DescribeMethod{
+		jmethods = append(jmethods, serial.DescribeMethod{
 			Name: meth.String(),
 			Pos:  fset.Position(meth.Obj().Pos()).String(),
 		})
diff --git a/oracle/freevars.go b/oracle/freevars.go
index 5e5d7548..d3e1af95 100644
--- a/oracle/freevars.go
+++ b/oracle/freevars.go
@@ -10,7 +10,7 @@ import (
 	"sort"
 
 	"code.google.com/p/go.tools/go/types"
-	"code.google.com/p/go.tools/oracle/json"
+	"code.google.com/p/go.tools/oracle/serial"
 )
 
 // freevars displays the lexical (not package-level) free variables of
@@ -169,11 +169,11 @@ func (r *freevarsResult) display(printf printfFunc) {
 	}
 }
 
-func (r *freevarsResult) toJSON(res *json.Result, fset *token.FileSet) {
-	var refs []*json.FreeVar
+func (r *freevarsResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	var refs []*serial.FreeVar
 	for _, ref := range r.refs {
 		refs = append(refs,
-			&json.FreeVar{
+			&serial.FreeVar{
 				Pos:  fset.Position(ref.obj.Pos()).String(),
 				Kind: ref.kind,
 				Ref:  ref.ref,
diff --git a/oracle/implements.go b/oracle/implements.go
index d26cd1ec..76b2e1fd 100644
--- a/oracle/implements.go
+++ b/oracle/implements.go
@@ -8,7 +8,7 @@ import (
 	"go/token"
 
 	"code.google.com/p/go.tools/go/types"
-	"code.google.com/p/go.tools/oracle/json"
+	"code.google.com/p/go.tools/oracle/serial"
 )
 
 // Implements displays the 'implements" relation among all
@@ -89,10 +89,10 @@ func (r *implementsResult) display(printf printfFunc) {
 	}
 }
 
-func (r *implementsResult) toJSON(res *json.Result, fset *token.FileSet) {
-	var facts []*json.Implements
+func (r *implementsResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	var facts []*serial.Implements
 	for _, fact := range r.facts {
-		facts = append(facts, &json.Implements{
+		facts = append(facts, &serial.Implements{
 			I:    fact.iface.String(),
 			IPos: fset.Position(fact.iface.Obj().Pos()).String(),
 			C:    fact.conc.String(),
diff --git a/oracle/oracle.go b/oracle/oracle.go
index 73239b92..2c9a33cd 100644
--- a/oracle/oracle.go
+++ b/oracle/oracle.go
@@ -18,7 +18,6 @@ package oracle
 
 import (
 	"bytes"
-	encjson "encoding/json"
 	"errors"
 	"fmt"
 	"go/ast"
@@ -34,7 +33,7 @@ import (
 
 	"code.google.com/p/go.tools/go/types"
 	"code.google.com/p/go.tools/importer"
-	"code.google.com/p/go.tools/oracle/json"
+	"code.google.com/p/go.tools/oracle/serial"
 	"code.google.com/p/go.tools/pointer"
 	"code.google.com/p/go.tools/ssa"
 )
@@ -97,7 +96,7 @@ type printfFunc func(pos interface{}, format string, args ...interface{})
 
 // queryResult is the interface of each query-specific result type.
 type queryResult interface {
-	toJSON(res *json.Result, fset *token.FileSet)
+	toSerial(res *serial.Result, fset *token.FileSet)
 	display(printf printfFunc)
 }
 
@@ -119,9 +118,6 @@ type QueryPos struct {
 }
 
 // A Result encapsulates the result of an oracle.Query.
-//
-// Result instances implement the json.Marshaler interface, i.e. they
-// can be JSON-serialized.
 type Result struct {
 	fset *token.FileSet
 	// fprintf is a closure over the oracle's fileset and start/end position.
@@ -131,16 +127,20 @@ type Result struct {
 	warnings []warning   // pointer analysis warnings
 }
 
-func (res *Result) MarshalJSON() ([]byte, error) {
-	resj := &json.Result{Mode: res.mode}
-	res.q.toJSON(resj, res.fset)
+// Serial returns an instance of serial.Result, which implements the
+// {xml,json}.Marshaler interfaces so that query results can be
+// serialized as JSON or XML.
+//
+func (res *Result) Serial() *serial.Result {
+	resj := &serial.Result{Mode: res.mode}
+	res.q.toSerial(resj, res.fset)
 	for _, w := range res.warnings {
-		resj.Warnings = append(resj.Warnings, json.PTAWarning{
+		resj.Warnings = append(resj.Warnings, serial.PTAWarning{
 			Pos:     res.fset.Position(w.pos).String(),
 			Message: fmt.Sprintf(w.format, w.args...),
 		})
 	}
-	return encjson.Marshal(resj)
+	return resj
 }
 
 // Query runs a single oracle query.
diff --git a/oracle/oracle_test.go b/oracle/oracle_test.go
index 337c85c6..e7934c70 100644
--- a/oracle/oracle_test.go
+++ b/oracle/oracle_test.go
@@ -175,17 +175,12 @@ func doQuery(out io.Writer, q *query, useJson bool) {
 
 	if useJson {
 		// JSON output
-		b, err := json.Marshal(res)
+		b, err := json.MarshalIndent(res.Serial(), "", "\t")
 		if err != nil {
 			fmt.Fprintf(out, "JSON error: %s\n", err.Error())
 			return
 		}
-		var buf bytes.Buffer
-		if err := json.Indent(&buf, b, "", "\t"); err != nil {
-			fmt.Fprintf(out, "json.Indent failed: %s", err)
-			return
-		}
-		out.Write(buf.Bytes())
+		out.Write(b)
 	} else {
 		// "plain" (compiler diagnostic format) output
 		capture := new(bytes.Buffer) // capture standard output
diff --git a/oracle/peers.go b/oracle/peers.go
index 09dba85d..1039331e 100644
--- a/oracle/peers.go
+++ b/oracle/peers.go
@@ -10,7 +10,7 @@ import (
 	"sort"
 
 	"code.google.com/p/go.tools/go/types"
-	"code.google.com/p/go.tools/oracle/json"
+	"code.google.com/p/go.tools/oracle/serial"
 	"code.google.com/p/go.tools/pointer"
 	"code.google.com/p/go.tools/ssa"
 )
@@ -174,8 +174,8 @@ func (r *peersResult) display(printf printfFunc) {
 	}
 }
 
-func (r *peersResult) toJSON(res *json.Result, fset *token.FileSet) {
-	peers := &json.Peers{
+func (r *peersResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	peers := &serial.Peers{
 		Pos:  fset.Position(r.queryPos).String(),
 		Type: r.queryType.String(),
 	}
diff --git a/oracle/referrers.go b/oracle/referrers.go
index 4bf16bd8..8ba9ffb9 100644
--- a/oracle/referrers.go
+++ b/oracle/referrers.go
@@ -10,7 +10,7 @@ import (
 	"sort"
 
 	"code.google.com/p/go.tools/go/types"
-	"code.google.com/p/go.tools/oracle/json"
+	"code.google.com/p/go.tools/oracle/serial"
 )
 
 // Referrers reports all identifiers that resolve to the same object
@@ -84,8 +84,8 @@ func (r *referrersResult) display(printf printfFunc) {
 	}
 }
 
-func (r *referrersResult) toJSON(res *json.Result, fset *token.FileSet) {
-	referrers := &json.Referrers{
+func (r *referrersResult) toSerial(res *serial.Result, fset *token.FileSet) {
+	referrers := &serial.Referrers{
 		Pos:  fset.Position(r.query).String(),
 		Desc: r.obj.String(),
 	}
diff --git a/oracle/json/json.go b/oracle/serial/serial.go
similarity index 98%
rename from oracle/json/json.go
rename to oracle/serial/serial.go
index be0d9963..ac1ee6d6 100644
--- a/oracle/json/json.go
+++ b/oracle/serial/serial.go
@@ -2,8 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package json defines the oracle's JSON schema.
-package json
+// Package serial defines the oracle's schema for structured data
+// serialization using JSON, XML, etc.
+package serial
 
 // All 'pos' strings are of the form "file:line:col".
 // TODO(adonovan): improve performance by sharing filename strings.