diff --git a/google/google.go b/google/google.go
index 422ff1f..41ced10 100644
--- a/google/google.go
+++ b/google/google.go
@@ -123,6 +123,7 @@
 	ServiceAccountImpersonationURL string                           `json:"service_account_impersonation_url"`
 	CredentialSource               externalaccount.CredentialSource `json:"credential_source"`
 	QuotaProjectID                 string                           `json:"quota_project_id"`
+	WorkforcePoolUserProject       string                           `json:"workforce_pool_user_project"`
 }
 
 func (f *credentialsFile) jwtConfig(scopes []string, subject string) *jwt.Config {
@@ -176,6 +177,7 @@
 			CredentialSource:               f.CredentialSource,
 			QuotaProjectID:                 f.QuotaProjectID,
 			Scopes:                         params.Scopes,
+			WorkforcePoolUserProject:       f.WorkforcePoolUserProject,
 		}
 		return cfg.TokenSource(ctx)
 	case "":
diff --git a/google/internal/externalaccount/basecredentials.go b/google/internal/externalaccount/basecredentials.go
index dab917f..a1e36c0 100644
--- a/google/internal/externalaccount/basecredentials.go
+++ b/google/internal/externalaccount/basecredentials.go
@@ -53,6 +53,11 @@
 	QuotaProjectID string
 	// Scopes contains the desired scopes for the returned access token.
 	Scopes []string
+	// The optional workforce pool user project number when the credential
+	// corresponds to a workforce pool and not a workload identity pool.
+	// The underlying principal must still have serviceusage.services.use IAM
+	// permission to use the project for billing/quota.
+	WorkforcePoolUserProject string
 }
 
 // Each element consists of a list of patterns.  validateURLs checks for matches
@@ -73,6 +78,7 @@
 		regexp.MustCompile(`^iamcredentials\.[^\.\s\/\\]+\.googleapis\.com$`),
 		regexp.MustCompile(`^[^\.\s\/\\]+-iamcredentials\.googleapis\.com$`),
 	}
+	validWorkforceAudiencePattern *regexp.Regexp = regexp.MustCompile(`//iam\.googleapis\.com/locations/[^/]+/workforcePools/`)
 )
 
 func validateURL(input string, patterns []*regexp.Regexp, scheme string) bool {
@@ -86,14 +92,17 @@
 	toTest := parsed.Host
 
 	for _, pattern := range patterns {
-
-		if valid := pattern.MatchString(toTest); valid {
+		if pattern.MatchString(toTest) {
 			return true
 		}
 	}
 	return false
 }
 
+func validateWorkforceAudience(input string) bool {
+	return validWorkforceAudiencePattern.MatchString(input)
+}
+
 // TokenSource Returns an external account TokenSource struct. This is to be called by package google to construct a google.Credentials.
 func (c *Config) TokenSource(ctx context.Context) (oauth2.TokenSource, error) {
 	return c.tokenSource(ctx, validTokenURLPatterns, validImpersonateURLPatterns, "https")
@@ -115,6 +124,13 @@
 		}
 	}
 
+	if c.WorkforcePoolUserProject != "" {
+		valid := validateWorkforceAudience(c.Audience)
+		if !valid {
+			return nil, fmt.Errorf("oauth2/google: workforce_pool_user_project should not be set for non-workforce pool credentials")
+		}
+	}
+
 	ts := tokenSource{
 		ctx:  ctx,
 		conf: c,
@@ -224,7 +240,15 @@
 		ClientID:     conf.ClientID,
 		ClientSecret: conf.ClientSecret,
 	}
-	stsResp, err := exchangeToken(ts.ctx, conf.TokenURL, &stsRequest, clientAuth, header, nil)
+	var options map[string]interface{}
+	// Do not pass workforce_pool_user_project when client authentication is used.
+	// The client ID is sufficient for determining the user project.
+	if conf.WorkforcePoolUserProject != "" && conf.ClientID == "" {
+		options = map[string]interface{}{
+			"userProject": conf.WorkforcePoolUserProject,
+		}
+	}
+	stsResp, err := exchangeToken(ts.ctx, conf.TokenURL, &stsRequest, clientAuth, header, options)
 	if err != nil {
 		return nil, err
 	}
diff --git a/google/internal/externalaccount/basecredentials_test.go b/google/internal/externalaccount/basecredentials_test.go
index b1131d6..5aa0d46 100644
--- a/google/internal/externalaccount/basecredentials_test.go
+++ b/google/internal/externalaccount/basecredentials_test.go
@@ -12,6 +12,8 @@
 	"strings"
 	"testing"
 	"time"
+
+	"golang.org/x/oauth2"
 )
 
 const (
@@ -35,55 +37,64 @@
 }
 
 var (
-	baseCredsRequestBody        = "audience=32555940559.apps.googleusercontent.com&grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange&requested_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aaccess_token&scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fdevstorage.full_control&subject_token=street123&subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Ajwt"
-	baseCredsResponseBody       = `{"access_token":"Sample.Access.Token","issued_token_type":"urn:ietf:params:oauth:token-type:access_token","token_type":"Bearer","expires_in":3600,"scope":"https://www.googleapis.com/auth/cloud-platform"}`
-	correctAT                   = "Sample.Access.Token"
-	expiry                int64 = 234852
+	baseCredsRequestBody                          = "audience=32555940559.apps.googleusercontent.com&grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange&requested_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aaccess_token&scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fdevstorage.full_control&subject_token=street123&subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aid_token"
+	baseCredsResponseBody                         = `{"access_token":"Sample.Access.Token","issued_token_type":"urn:ietf:params:oauth:token-type:access_token","token_type":"Bearer","expires_in":3600,"scope":"https://www.googleapis.com/auth/cloud-platform"}`
+	workforcePoolRequestBodyWithClientId          = "audience=%2F%2Fiam.googleapis.com%2Flocations%2Feu%2FworkforcePools%2Fpool-id%2Fproviders%2Fprovider-id&grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange&requested_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aaccess_token&scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fdevstorage.full_control&subject_token=street123&subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aid_token"
+	workforcePoolRequestBodyWithoutClientId       = "audience=%2F%2Fiam.googleapis.com%2Flocations%2Feu%2FworkforcePools%2Fpool-id%2Fproviders%2Fprovider-id&grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange&options=%7B%22userProject%22%3A%22myProject%22%7D&requested_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aaccess_token&scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fdevstorage.full_control&subject_token=street123&subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aid_token"
+	correctAT                                     = "Sample.Access.Token"
+	expiry                                  int64 = 234852
 )
 var (
 	testNow = func() time.Time { return time.Unix(expiry, 0) }
 )
 
-func TestToken(t *testing.T) {
+type testExchangeTokenServer struct {
+	url           string
+	authorization string
+	contentType   string
+	body          string
+	response      string
+}
 
-	targetServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if got, want := r.URL.String(), "/"; got != want {
+func run(t *testing.T, config *Config, tets *testExchangeTokenServer) (*oauth2.Token, error) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if got, want := r.URL.String(), tets.url; got != want {
 			t.Errorf("URL.String(): got %v but want %v", got, want)
 		}
 		headerAuth := r.Header.Get("Authorization")
-		if got, want := headerAuth, "Basic cmJyZ25vZ25yaG9uZ28zYmk0Z2I5Z2hnOWc6bm90c29zZWNyZXQ="; got != want {
+		if got, want := headerAuth, tets.authorization; got != want {
 			t.Errorf("got %v but want %v", got, want)
 		}
 		headerContentType := r.Header.Get("Content-Type")
-		if got, want := headerContentType, "application/x-www-form-urlencoded"; got != want {
+		if got, want := headerContentType, tets.contentType; got != want {
 			t.Errorf("got %v but want %v", got, want)
 		}
 		body, err := ioutil.ReadAll(r.Body)
 		if err != nil {
 			t.Fatalf("Failed reading request body: %s.", err)
 		}
-		if got, want := string(body), baseCredsRequestBody; got != want {
+		if got, want := string(body), tets.body; got != want {
 			t.Errorf("Unexpected exchange payload: got %v but want %v", got, want)
 		}
 		w.Header().Set("Content-Type", "application/json")
-		w.Write([]byte(baseCredsResponseBody))
+		w.Write([]byte(tets.response))
 	}))
-	defer targetServer.Close()
-
-	testConfig.TokenURL = targetServer.URL
-	ourTS := tokenSource{
-		ctx:  context.Background(),
-		conf: &testConfig,
-	}
+	defer server.Close()
+	config.TokenURL = server.URL
 
 	oldNow := now
 	defer func() { now = oldNow }()
 	now = testNow
 
-	tok, err := ourTS.Token()
-	if err != nil {
-		t.Fatalf("Unexpected error: %e", err)
+	ts := tokenSource{
+		ctx:  context.Background(),
+		conf: config,
 	}
+
+	return ts.Token()
+}
+
+func validateToken(t *testing.T, tok *oauth2.Token) {
 	if got, want := tok.AccessToken, correctAT; got != want {
 		t.Errorf("Unexpected access token: got %v, but wanted %v", got, want)
 	}
@@ -91,10 +102,110 @@
 		t.Errorf("Unexpected TokenType: got %v, but wanted %v", got, want)
 	}
 
-	if got, want := tok.Expiry, now().Add(time.Duration(3600)*time.Second); got != want {
+	if got, want := tok.Expiry, testNow().Add(time.Duration(3600)*time.Second); got != want {
 		t.Errorf("Unexpected Expiry: got %v, but wanted %v", got, want)
 	}
+}
 
+func TestToken(t *testing.T) {
+	config := Config{
+		Audience:         "32555940559.apps.googleusercontent.com",
+		SubjectTokenType: "urn:ietf:params:oauth:token-type:id_token",
+		ClientSecret:     "notsosecret",
+		ClientID:         "rbrgnognrhongo3bi4gb9ghg9g",
+		CredentialSource: testBaseCredSource,
+		Scopes:           []string{"https://www.googleapis.com/auth/devstorage.full_control"},
+	}
+
+	server := testExchangeTokenServer{
+		url:           "/",
+		authorization: "Basic cmJyZ25vZ25yaG9uZ28zYmk0Z2I5Z2hnOWc6bm90c29zZWNyZXQ=",
+		contentType:   "application/x-www-form-urlencoded",
+		body:          baseCredsRequestBody,
+		response:      baseCredsResponseBody,
+	}
+
+	tok, err := run(t, &config, &server)
+
+	if err != nil {
+		t.Fatalf("Unexpected error: %e", err)
+	}
+	validateToken(t, tok)
+}
+
+func TestWorkforcePoolTokenWithClientID(t *testing.T) {
+	config := Config{
+		Audience:                 "//iam.googleapis.com/locations/eu/workforcePools/pool-id/providers/provider-id",
+		SubjectTokenType:         "urn:ietf:params:oauth:token-type:id_token",
+		ClientSecret:             "notsosecret",
+		ClientID:                 "rbrgnognrhongo3bi4gb9ghg9g",
+		CredentialSource:         testBaseCredSource,
+		Scopes:                   []string{"https://www.googleapis.com/auth/devstorage.full_control"},
+		WorkforcePoolUserProject: "myProject",
+	}
+
+	server := testExchangeTokenServer{
+		url:           "/",
+		authorization: "Basic cmJyZ25vZ25yaG9uZ28zYmk0Z2I5Z2hnOWc6bm90c29zZWNyZXQ=",
+		contentType:   "application/x-www-form-urlencoded",
+		body:          workforcePoolRequestBodyWithClientId,
+		response:      baseCredsResponseBody,
+	}
+
+	tok, err := run(t, &config, &server)
+
+	if err != nil {
+		t.Fatalf("Unexpected error: %e", err)
+	}
+	validateToken(t, tok)
+}
+
+func TestWorkforcePoolTokenWithoutClientID(t *testing.T) {
+	config := Config{
+		Audience:                 "//iam.googleapis.com/locations/eu/workforcePools/pool-id/providers/provider-id",
+		SubjectTokenType:         "urn:ietf:params:oauth:token-type:id_token",
+		ClientSecret:             "notsosecret",
+		CredentialSource:         testBaseCredSource,
+		Scopes:                   []string{"https://www.googleapis.com/auth/devstorage.full_control"},
+		WorkforcePoolUserProject: "myProject",
+	}
+
+	server := testExchangeTokenServer{
+		url:           "/",
+		authorization: "",
+		contentType:   "application/x-www-form-urlencoded",
+		body:          workforcePoolRequestBodyWithoutClientId,
+		response:      baseCredsResponseBody,
+	}
+
+	tok, err := run(t, &config, &server)
+
+	if err != nil {
+		t.Fatalf("Unexpected error: %e", err)
+	}
+	validateToken(t, tok)
+}
+
+func TestNonworkforceWithWorkforcePoolUserProject(t *testing.T) {
+	config := Config{
+		Audience:                 "32555940559.apps.googleusercontent.com",
+		SubjectTokenType:         "urn:ietf:params:oauth:token-type:id_token",
+		TokenURL:                 "https://sts.googleapis.com",
+		ClientSecret:             "notsosecret",
+		ClientID:                 "rbrgnognrhongo3bi4gb9ghg9g",
+		CredentialSource:         testBaseCredSource,
+		Scopes:                   []string{"https://www.googleapis.com/auth/devstorage.full_control"},
+		WorkforcePoolUserProject: "myProject",
+	}
+
+	_, err := config.TokenSource(context.Background())
+
+	if err == nil {
+		t.Fatalf("Expected error but found none")
+	}
+	if got, want := err.Error(), "oauth2/google: workforce_pool_user_project should not be set for non-workforce pool credentials"; got != want {
+		t.Errorf("Incorrect error received.\nExpected: %s\nRecieved: %s", want, got)
+	}
 }
 
 func TestValidateURLTokenURL(t *testing.T) {
@@ -210,3 +321,41 @@
 		})
 	}
 }
+
+func TestWorkforcePoolCreation(t *testing.T) {
+	var audienceValidatyTests = []struct {
+		audience      string
+		expectSuccess bool
+	}{
+		{"//iam.googleapis.com/locations/global/workforcePools/pool-id/providers/provider-id", true},
+		{"//iam.googleapis.com/locations/eu/workforcePools/pool-id/providers/provider-id", true},
+		{"//iam.googleapis.com/locations/eu/workforcePools/workloadIdentityPools/providers/provider-id", true},
+		{"identitynamespace:1f12345:my_provider", false},
+		{"//iam.googleapis.com/projects/123456/locations/global/workloadIdentityPools/pool-id/providers/provider-id", false},
+		{"//iam.googleapis.com/projects/123456/locations/eu/workloadIdentityPools/pool-id/providers/provider-id", false},
+		{"//iam.googleapis.com/projects/123456/locations/global/workloadIdentityPools/workforcePools/providers/provider-id", false},
+		{"//iamgoogleapis.com/locations/eu/workforcePools/pool-id/providers/provider-id", false},
+		{"//iam.googleapiscom/locations/eu/workforcePools/pool-id/providers/provider-id", false},
+		{"//iam.googleapis.com/locations/workforcePools/pool-id/providers/provider-id", false},
+		{"//iam.googleapis.com/locations/eu/workforcePool/pool-id/providers/provider-id", false},
+		{"//iam.googleapis.com/locations//workforcePool/pool-id/providers/provider-id", false},
+	}
+
+	ctx := context.Background()
+	for _, tt := range audienceValidatyTests {
+		t.Run(" "+tt.audience, func(t *testing.T) { // We prepend a space ahead of the test input when outputting for sake of readability.
+			config := testConfig
+			config.TokenURL = "https://sts.googleapis.com" // Setting the most basic acceptable tokenURL
+			config.ServiceAccountImpersonationURL = "https://iamcredentials.googleapis.com"
+			config.Audience = tt.audience
+			config.WorkforcePoolUserProject = "myProject"
+			_, err := config.TokenSource(ctx)
+
+			if tt.expectSuccess && err != nil {
+				t.Errorf("got %v but want nil", err)
+			} else if !tt.expectSuccess && err == nil {
+				t.Errorf("got nil but expected an error")
+			}
+		})
+	}
+}