diff --git a/internal/driver/testdata/pprof.cpu.flat.addresses.weblist b/internal/driver/testdata/pprof.cpu.flat.addresses.weblist
index 743b68ec..4c4a6d1a 100644
--- a/internal/driver/testdata/pprof.cpu.flat.addresses.weblist
+++ b/internal/driver/testdata/pprof.cpu.flat.addresses.weblist
@@ -37,6 +37,12 @@ background-color: #eeeeee;
 color: #008800;
 display: none;
 }
+.ptile_95 {
+background-color: #fe5252
+}
+.ptile_80 {
+background-color: #ffb6c1
+}
 </style>
 <script type="text/javascript">
 function pprof_toggle_asm(e) {
@@ -63,41 +69,41 @@ Type: cpu<br>
 Duration: 10s, Total samples = 1.12s (11.20%)<br>Total: 1.12s</div><h2>line1000</h2><p class="filename">testdata/file1000.src</p>
 <pre onClick="pprof_toggle_asm(event)">
   Total:       1.10s      1.10s (flat, cum) 98.21%
-<span class=line>      1</span> <span class=deadsrc>       1.10s      1.10s           line1 </span><span class=asm>               1.10s      1.10s     1000:     instruction one                                                              <span class=unimportant>file1000.src:1</span>
+<span class=line>      1</span> <span class="deadsrc ptile_80">       1.10s      1.10s           line1 </span><span class=asm>               1.10s      1.10s     1000:     instruction one                                                              <span class=unimportant>file1000.src:1</span>
                    .          .     1001:     instruction two                                                              <span class=unimportant>file1000.src:1</span>
                                      ⋮
                    .          .     1003:     instruction four                                                             <span class=unimportant>file1000.src:1</span>
 </span>
-<span class=line>      2</span> <span class=deadsrc>           .          .           line2 </span><span class=asm>                   .          .     1002:     instruction three                                                            <span class=unimportant>file1000.src:2</span>
+<span class=line>      2</span> <span class="deadsrc">           .          .           line2 </span><span class=asm>                   .          .     1002:     instruction three                                                            <span class=unimportant>file1000.src:2</span>
 </span>
-<span class=line>      3</span> <span class=nop>           .          .           line3 </span>
-<span class=line>      4</span> <span class=nop>           .          .           line4 </span>
-<span class=line>      5</span> <span class=nop>           .          .           line5 </span>
-<span class=line>      6</span> <span class=nop>           .          .           line6 </span>
-<span class=line>      7</span> <span class=nop>           .          .           line7 </span>
+<span class=line>      3</span> <span class="nop">           .          .           line3 </span>
+<span class=line>      4</span> <span class="nop">           .          .           line4 </span>
+<span class=line>      5</span> <span class="nop">           .          .           line5 </span>
+<span class=line>      6</span> <span class="nop">           .          .           line6 </span>
+<span class=line>      7</span> <span class="nop">           .          .           line7 </span>
 </pre>
 <h2>line3000</h2><p class="filename">testdata/file3000.src</p>
 <pre onClick="pprof_toggle_asm(event)">
   Total:        10ms      1.12s (flat, cum)   100%
-<span class=line>      1</span> <span class=nop>           .          .           line1 </span>
-<span class=line>      2</span> <span class=nop>           .          .           line2 </span>
-<span class=line>      3</span> <span class=nop>           .          .           line3 </span>
-<span class=line>      4</span> <span class=nop>           .          .           line4 </span>
-<span class=line>      5</span> <span class=nop>           .          .           line5 </span>
-<span class=line>      6</span> <span class=deadsrc>        10ms      1.01s           line6 </span><span class=asm>                10ms      1.01s     3000:     instruction one                                                              <span class=unimportant>file3000.src:6</span>
+<span class=line>      1</span> <span class="nop">           .          .           line1 </span>
+<span class=line>      2</span> <span class="nop">           .          .           line2 </span>
+<span class=line>      3</span> <span class="nop">           .          .           line3 </span>
+<span class=line>      4</span> <span class="nop">           .          .           line4 </span>
+<span class=line>      5</span> <span class="nop">           .          .           line5 </span>
+<span class=line>      6</span> <span class="deadsrc ptile_80">        10ms      1.01s           line6 </span><span class=asm>                10ms      1.01s     3000:     instruction one                                                              <span class=unimportant>file3000.src:6</span>
 </span>
-<span class=line>      7</span> <span class=nop>           .          .           line7 </span>
-<span class=line>      8</span> <span class=nop>           .          .           line8 </span>
-<span class=line>      9</span> <span class=deadsrc>           .      110ms           line9 </span><span class=asm>                   .      100ms     3001:     instruction two                                                              <span class=unimportant>file3000.src:9</span>
+<span class=line>      7</span> <span class="nop">           .          .           line7 </span>
+<span class=line>      8</span> <span class="nop">           .          .           line8 </span>
+<span class=line>      9</span> <span class="deadsrc ptile_80">           .      110ms           line9 </span><span class=asm>                   .      100ms     3001:     instruction two                                                              <span class=unimportant>file3000.src:9</span>
                    .       10ms     3002:     instruction three                                                            <span class=unimportant>file3000.src:9</span>
                    .          .     3003:     instruction four                                                             <span class=unimportant></span>
                    .          .     3004:     instruction five                                                             <span class=unimportant></span>
 </span>
-<span class=line>     10</span> <span class=nop>           .          .           line0 </span>
-<span class=line>     11</span> <span class=nop>           .          .           line1 </span>
-<span class=line>     12</span> <span class=nop>           .          .           line2 </span>
-<span class=line>     13</span> <span class=nop>           .          .           line3 </span>
-<span class=line>     14</span> <span class=nop>           .          .           line4 </span>
+<span class=line>     10</span> <span class="nop">           .          .           line0 </span>
+<span class=line>     11</span> <span class="nop">           .          .           line1 </span>
+<span class=line>     12</span> <span class="nop">           .          .           line2 </span>
+<span class=line>     13</span> <span class="nop">           .          .           line3 </span>
+<span class=line>     14</span> <span class="nop">           .          .           line4 </span>
 </pre>
 
 </body>
diff --git a/internal/report/source.go b/internal/report/source.go
index b4805354..3a36f86d 100644
--- a/internal/report/source.go
+++ b/internal/report/source.go
@@ -24,6 +24,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"sort"
 	"strconv"
 	"strings"
 
@@ -214,14 +215,66 @@ func PrintWebList(w io.Writer, rpt *Report, obj plugin.ObjTool, maxFiles int) er
 		}
 
 		printFunctionHeader(w, ff.functionName, path, n.Flat, n.Cum, rpt)
+		ptiles := calculatePtiles(fnodes)
 		for _, fn := range fnodes {
-			printFunctionSourceLine(w, fn, asm[fn.Info.Lineno], reader, rpt)
+			printFunctionSourceLine(w, fn, asm[fn.Info.Lineno], reader, getPtileCSSClassName(fn.Cum, ptiles), rpt)
 		}
 		printFunctionClosing(w)
 	}
 	return nil
 }
 
+func getPtileCSSClassName(cumSum int64, ptiles map[int64]int64) string {
+	if cumSum == 0 {
+		return ""
+	}
+	for key, value := range ptiles {
+		if cumSum > value {
+			return " ptile_" + strconv.FormatInt(key, 10)
+		}
+	}
+	return ""
+}
+
+// calculatePtile expects cumSums to be sorted and
+// to contain unique elements. It also expects the ptile to be between 0 and 99.
+func calculatePtile(ptile int64, cumSums []int64) int64 {
+	rank := float64(ptile) / 100 * float64(len(cumSums))
+	return cumSums[int64(rank)]
+}
+
+func getArrayOfCumValues(fnodes graph.Nodes) []int64 {
+	arrayOfCumValues := make([]int64, 0, len(fnodes))
+
+	for _, fn := range fnodes {
+		arrayOfCumValues = append(arrayOfCumValues, fn.Cum)
+	}
+
+	return arrayOfCumValues
+}
+
+type int64Slice []int64
+
+func (a int64Slice) Len() int           { return len(a) }
+func (a int64Slice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a int64Slice) Less(i, j int) bool { return a[i] < a[j] }
+
+// calculatePtiles returns nil when the fnodes length is 0
+// because its result will never be used in such a case.
+func calculatePtiles(fnodes graph.Nodes) map[int64]int64 {
+	if len(fnodes) == 0 {
+		return nil
+	}
+	arrayOfCumValues := getArrayOfCumValues(fnodes)
+	ptiles := map[int64]int64{95: 0, 80: 0}
+	sort.Sort(int64Slice(arrayOfCumValues))
+	for key := range ptiles {
+		ptiles[key] = calculatePtile(key, arrayOfCumValues)
+	}
+
+	return ptiles
+}
+
 // sourceCoordinates returns the lowest and highest line numbers from
 // a set of assembly statements.
 func sourceCoordinates(asm map[int][]assemblyInstruction) (start, end int) {
@@ -348,19 +401,21 @@ func printFunctionHeader(w io.Writer, name, path string, flatSum, cumSum int64,
 }
 
 // printFunctionSourceLine prints a source line and the corresponding assembly.
-func printFunctionSourceLine(w io.Writer, fn *graph.Node, assembly []assemblyInstruction, reader *sourceReader, rpt *Report) {
+func printFunctionSourceLine(w io.Writer, fn *graph.Node, assembly []assemblyInstruction, reader *sourceReader, ptileCSSClassName string, rpt *Report) {
 	if len(assembly) == 0 {
 		fmt.Fprintf(w,
-			"<span class=line> %6d</span> <span class=nop>  %10s %10s %8s  %s </span>\n",
+			"<span class=line> %6d</span> <span class=\"nop%s\">  %10s %10s %8s  %s </span>\n",
 			fn.Info.Lineno,
+			ptileCSSClassName,
 			valueOrDot(fn.Flat, rpt), valueOrDot(fn.Cum, rpt),
 			"", template.HTMLEscapeString(fn.Info.Name))
 		return
 	}
 
 	fmt.Fprintf(w,
-		"<span class=line> %6d</span> <span class=deadsrc>  %10s %10s %8s  %s </span>",
+		"<span class=line> %6d</span> <span class=\"deadsrc%s\">  %10s %10s %8s  %s </span>",
 		fn.Info.Lineno,
+		ptileCSSClassName,
 		valueOrDot(fn.Flat, rpt), valueOrDot(fn.Cum, rpt),
 		"", template.HTMLEscapeString(fn.Info.Name))
 	srcIndent := indentation(fn.Info.Name)
diff --git a/internal/report/source_html.go b/internal/report/source_html.go
index 26e8bdbb..a6b88527 100644
--- a/internal/report/source_html.go
+++ b/internal/report/source_html.go
@@ -57,6 +57,12 @@ background-color: #eeeeee;
 color: #008800;
 display: none;
 }
+.ptile_95 {
+background-color: #fe5252
+}
+.ptile_80 {
+background-color: #ffb6c1
+}
 </style>`
 
 const weblistPageScript = `<script type="text/javascript">
diff --git a/internal/report/source_test.go b/internal/report/source_test.go
index c6e179c7..f8e2c744 100644
--- a/internal/report/source_test.go
+++ b/internal/report/source_test.go
@@ -19,15 +19,89 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"reflect"
 	"regexp"
 	"runtime"
+	"strconv"
 	"strings"
 	"testing"
 
 	"github.com/google/pprof/internal/binutils"
+	"github.com/google/pprof/internal/graph"
 	"github.com/google/pprof/profile"
 )
 
+type prettyNodes graph.Nodes
+
+func (nodes prettyNodes) String() string {
+	strs := make([]string, 0, len(nodes)+2)
+	strs = append(strs, "[")
+	for _, node := range nodes {
+		strs = append(strs, "Cum: "+strconv.FormatInt(node.Cum, 10))
+	}
+	strs = append(strs, "]")
+	return strings.Join(strs, " ")
+}
+
+func TestCalculatePtiles(t *testing.T) {
+	for _, testCase := range []struct {
+		nodes graph.Nodes
+		want  map[int64]int64
+	}{
+		{
+			nodes: nil,
+			want:  nil,
+		},
+		{
+			nodes: []*graph.Node{
+				{Cum: 0},
+				{Cum: 8},
+			},
+			want: map[int64]int64{80: 8, 95: 8},
+		},
+		{
+			nodes: []*graph.Node{
+				{Cum: 10},
+				{Cum: 5},
+				{Cum: 8},
+			},
+			want: map[int64]int64{80: 10, 95: 10},
+		},
+		{
+			nodes: []*graph.Node{
+				{Cum: 0},
+				{Cum: 0},
+				{Cum: 0},
+				{Cum: 0},
+				{Cum: 11},
+				{Cum: 2},
+				{Cum: 9},
+				{Cum: 4},
+				{Cum: 8},
+				{Cum: 2},
+				{Cum: 16},
+				{Cum: 22},
+				{Cum: 13},
+			},
+			want: map[int64]int64{80: 13, 95: 22},
+		},
+		{
+			nodes: []*graph.Node{
+				{Cum: 10},
+				{Cum: 10},
+				{Cum: 10},
+				{Cum: 10},
+				{Cum: 10},
+			},
+			want: map[int64]int64{80: 10, 95: 10},
+		},
+	} {
+		if ptiles := calculatePtiles(testCase.nodes); !reflect.DeepEqual(ptiles, testCase.want) {
+			t.Errorf("calculatePtiles(%v) = %v; want %v", prettyNodes(testCase.nodes), ptiles, testCase.want)
+		}
+	}
+}
+
 func TestWebList(t *testing.T) {
 	if runtime.GOOS != "linux" || runtime.GOARCH != "amd64" {
 		t.Skip("weblist only tested on x86-64 linux")