diff --git a/spanner/src/isolation_level.php b/spanner/src/isolation_level.php
new file mode 100644
index 000000000..778d101b8
--- /dev/null
+++ b/spanner/src/isolation_level.php
@@ -0,0 +1,74 @@
+<?php
+/**
+ * Copyright 2026 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * For instructions on how to run the full sample:
+ *
+ * @see https://github.com/GoogleCloudPlatform/php-docs-samples/tree/main/spanner/README.md
+ */
+
+namespace Google\Cloud\Samples\Spanner;
+
+// [START spanner_isolation_level]
+use Google\Cloud\Spanner\SpannerClient;
+use Google\Cloud\Spanner\Transaction;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
+
+/**
+ * Shows how to run a Read Write transaction with isolation level options.
+ *
+ * Example:
+ * ```
+ * isolation_level($instanceId, $databaseId);
+ * ```
+ *
+ * @param string $instanceId The Spanner instance ID.
+ * @param string $databaseId The Spanner database ID.
+ */
+function isolation_level(string $instanceId, string $databaseId): void
+{
+    // The isolation level specified at the client-level will be applied to all
+    // RW transactions.
+    $spanner = new SpannerClient([
+        'isolationLevel' => IsolationLevel::SERIALIZABLE
+    ]);
+    $instance = $spanner->instance($instanceId);
+    $database = $instance->database($databaseId);
+
+    // The isolation level specified at the request level takes precedence over
+    // the isolation level configured at the client level.
+    $database->runTransaction(function (Transaction $t) {
+        // Read an AlbumTitle.
+        $results = $t->execute('SELECT AlbumTitle from Albums WHERE SingerId = 1 and AlbumId = 1');
+        foreach ($results as $row) {
+            printf('Current Album Title: %s' . PHP_EOL, $row['AlbumTitle']);
+        }
+
+        // Update the AlbumTitle.
+        $rowCount = $t->executeUpdate('UPDATE Albums SET AlbumTitle = \'A New Title\' WHERE SingerId = 1 and AlbumId = 1');
+        printf('%d record(s) updated.' . PHP_EOL, $rowCount);
+    }, [
+        'transactionOptions' => [
+            'isolationLevel' => IsolationLevel::REPEATABLE_READ
+        ]
+    ]);
+}
+// [END spanner_isolation_level]
+
+// The following 2 lines are only needed to run the samples
+require_once __DIR__ . '/../../testing/sample_helpers.php';
+\Google\Cloud\Samples\execute_sample(__FILE__, __NAMESPACE__, $argv);
diff --git a/spanner/src/read_lock_mode.php b/spanner/src/read_lock_mode.php
new file mode 100644
index 000000000..1e3bf115a
--- /dev/null
+++ b/spanner/src/read_lock_mode.php
@@ -0,0 +1,74 @@
+<?php
+/**
+ * Copyright 2026 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * For instructions on how to run the full sample:
+ *
+ * @see https://github.com/GoogleCloudPlatform/php-docs-samples/tree/main/spanner/README.md
+ */
+
+namespace Google\Cloud\Samples\Spanner;
+
+// [START spanner_read_lock_mode]
+use Google\Cloud\Spanner\SpannerClient;
+use Google\Cloud\Spanner\Transaction;
+use Google\Cloud\Spanner\V1\TransactionOptions\ReadWrite\ReadLockMode;
+
+/**
+ * Shows how to run a Read Write transaction with read lock mode options.
+ *
+ * Example:
+ * ```
+ * read_lock_mode($instanceId, $databaseId);
+ * ```
+ *
+ * @param string $instanceId The Spanner instance ID.
+ * @param string $databaseId The Spanner database ID.
+ */
+function read_lock_mode(string $instanceId, string $databaseId): void
+{
+    // The read lock mode specified at the client-level will be applied to all
+    // RW transactions.
+    $spanner = new SpannerClient([
+        'readLockMode' => ReadLockMode::OPTIMISTIC
+    ]);
+    $instance = $spanner->instance($instanceId);
+    $database = $instance->database($databaseId);
+
+    // The read lock mode specified at the request level takes precedence over
+    // the read lock mode configured at the client level.
+    $database->runTransaction(function (Transaction $t) {
+        // Read an AlbumTitle.
+        $results = $t->execute('SELECT AlbumTitle from Albums WHERE SingerId = 2 and AlbumId = 1');
+        foreach ($results as $row) {
+            printf('Current Album Title: %s' . PHP_EOL, $row['AlbumTitle']);
+        }
+
+        // Update the AlbumTitle.
+        $rowCount = $t->executeUpdate('UPDATE Albums SET AlbumTitle = \'A New Title\' WHERE SingerId = 2 and AlbumId = 1');
+        printf('%d record(s) updated.' . PHP_EOL, $rowCount);
+    }, [
+        'transactionOptions' => [
+            'readLockMode' => ReadLockMode::PESSIMISTIC
+        ]
+    ]);
+}
+// [END spanner_read_lock_mode]
+
+// The following 2 lines are only needed to run the samples
+require_once __DIR__ . '/../../testing/sample_helpers.php';
+\Google\Cloud\Samples\execute_sample(__FILE__, __NAMESPACE__, $argv);
diff --git a/spanner/test/spannerTest.php b/spanner/test/spannerTest.php
index 548042e6c..0b86844ce 100644
--- a/spanner/test/spannerTest.php
+++ b/spanner/test/spannerTest.php
@@ -492,6 +492,26 @@ public function testReadWriteTransaction()
         $this->assertStringContainsString('Transaction complete.', $output);
     }
 
+    /**
+     * @depends testUpdateData
+     */
+    public function testReadLockMode()
+    {
+        $output = $this->runFunctionSnippet('read_lock_mode');
+        $this->assertStringContainsString('Current Album Title:', $output);
+        $this->assertStringContainsString('record(s) updated.', $output);
+    }
+
+    /**
+     * @depends testUpdateData
+     */
+    public function testIsolationLevel()
+    {
+        $output = $this->runFunctionSnippet('isolation_level');
+        $this->assertStringContainsString('Current Album Title:', $output);
+        $this->assertStringContainsString('record(s) updated.', $output);
+    }
+
     /**
      * @depends testAddColumn
      */