diff --git a/README.md b/README.md
index 16966ffe..fe8fd8aa 100644
--- a/README.md
+++ b/README.md
@@ -217,7 +217,7 @@ Now you're ready to go!
 | `runner-home-dir`                                                                                                                                                              | Optional. Used only with the `start` mode. | Specifies a directory where pre-installed actions-runner software and scripts are located.<br><br> |
 | `pre-runner-script`                                                                                                                                                              | Optional. Used only with the `start` mode. | Specifies bash commands to run before the runner starts.  It's useful for installing dependencies with apt-get, yum, dnf, etc. For example:<pre>          - name: Start EC2 runner<br>            with:<br>              mode: start<br>              ...<br>              pre-runner-script: \|<br>                 sudo yum update -y && \ <br>                 sudo yum install docker git libicu -y<br>                 sudo systemctl enable docker</pre> |
 | `market-type` | Optional. Used only with the `start` mode. | This field accepts only the value `spot`. <br><br> If set to `spot`, the runner will be launched as a Spot instance. <br><br> If omitted, the runner will be launched as an on-demand instance. |
-| `block-device-mappings` | Optional. Used only with the `start` mode. | JSON string specifying the block device mappings for the EC2 instance. For example: <br> <pre>[{"DeviceName": "/dev/sda1", "Ebs": {"VolumeSize": 100, "VolumeType": "gp3"}}]</pre> See <a href="https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_BlockDeviceMapping.html">AWS BlockDeviceMapping docs</a> for all options. |
+| `block-device-mappings` | Optional. Used only with the `start` mode. | JSON string specifying the block device mappings for the EC2 instance. For example: <br> <pre>[{"DeviceName": "/dev/sda1", "Ebs": {"VolumeSize": 100, "VolumeType": "gp3"}}]</pre> See <a href="https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_BlockDeviceMapping.html">AWS BlockDeviceMapping docs</a> for all options. <br><br> **Note on EBS Volume Deletion**: All EBS volumes are automatically configured with `DeleteOnTermination: true` to prevent orphaned volumes and unexpected costs. The action will add this property to any volume that doesn't explicitly set it. If you explicitly set `DeleteOnTermination: false`, that setting will be respected. |
 | `startup-quiet-period-seconds` | Optional | Default: 30 |
 | `startup-retry-interval-seconds` | Optional | Default: 10 |
 | `startup-timeout-minutes` | Optional | Default: 5 |
@@ -286,6 +286,8 @@ jobs:
             [
               {"DeviceName": "/dev/sda1", "Ebs": {"VolumeSize": 100, "VolumeType": "gp3"}}
             ]
+          # Note: To preserve a volume after instance termination, explicitly set DeleteOnTermination: false:
+          #     {"DeviceName": "/dev/sdb", "Ebs": {"VolumeSize": 50, "DeleteOnTermination": false}}
   do-the-job:
     name: Do the job on the runner
     needs: start-runner # required to start the main job when the runner is ready
diff --git a/dist/index.js b/dist/index.js
index 7e20435b..85a87a9a 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -145115,6 +145115,38 @@ function buildMarketOptions() {
   };
 }
 
+/**
+ * Ensures all block device mappings have DeleteOnTermination set to true.
+ * Respects explicit user settings if DeleteOnTermination is already defined.
+ *
+ * @param {Array} blockDeviceMappings - Array of BlockDeviceMapping objects
+ * @returns {Array} Modified array with DeleteOnTermination set appropriately
+ */
+function ensureDeleteOnTermination(blockDeviceMappings) {
+  if (!Array.isArray(blockDeviceMappings) || blockDeviceMappings.length === 0) {
+    return blockDeviceMappings;
+  }
+
+  return blockDeviceMappings.map(mapping => {
+    // Create a shallow copy to avoid mutating the original
+    const modifiedMapping = { ...mapping };
+
+    // Only process if the mapping has an Ebs configuration
+    if (modifiedMapping.Ebs) {
+      // Create a shallow copy of the Ebs object
+      modifiedMapping.Ebs = { ...modifiedMapping.Ebs };
+
+      // Only set DeleteOnTermination if it's not already explicitly defined
+      // This respects user's explicit choice if they set it to false
+      if (modifiedMapping.Ebs.DeleteOnTermination === undefined) {
+        modifiedMapping.Ebs.DeleteOnTermination = true;
+      }
+    }
+
+    return modifiedMapping;
+  });
+}
+
 async function createEc2InstanceWithParams(imageId, subnetId, securityGroupId, label, githubRegistrationToken, region) {
   // Region is always specified now, so we can directly use it
   const ec2ClientOptions = { region };
@@ -145143,13 +145175,14 @@ async function createEc2InstanceWithParams(imageId, subnetId, securityGroupId, l
         Ebs: {
           ...(config.input.ec2VolumeSize !== '' && { VolumeSize: config.input.ec2VolumeSize }),
           ...(config.input.ec2VolumeType !== '' && { VolumeType: config.input.ec2VolumeType }),
+          DeleteOnTermination: true,
         },
       },
     ];
   }
 
   if (config.input.blockDeviceMappings.length > 0) {
-    params.BlockDeviceMappings = config.input.blockDeviceMappings;
+    params.BlockDeviceMappings = ensureDeleteOnTermination(config.input.blockDeviceMappings);
   }
 
   const result = await ec2.send(new RunInstancesCommand(params));
diff --git a/src/aws.js b/src/aws.js
index 80afacfa..afe5a29c 100644
--- a/src/aws.js
+++ b/src/aws.js
@@ -107,6 +107,38 @@ function buildMarketOptions() {
   };
 }
 
+/**
+ * Ensures all block device mappings have DeleteOnTermination set to true.
+ * Respects explicit user settings if DeleteOnTermination is already defined.
+ *
+ * @param {Array} blockDeviceMappings - Array of BlockDeviceMapping objects
+ * @returns {Array} Modified array with DeleteOnTermination set appropriately
+ */
+function ensureDeleteOnTermination(blockDeviceMappings) {
+  if (!Array.isArray(blockDeviceMappings) || blockDeviceMappings.length === 0) {
+    return blockDeviceMappings;
+  }
+
+  return blockDeviceMappings.map(mapping => {
+    // Create a shallow copy to avoid mutating the original
+    const modifiedMapping = { ...mapping };
+
+    // Only process if the mapping has an Ebs configuration
+    if (modifiedMapping.Ebs) {
+      // Create a shallow copy of the Ebs object
+      modifiedMapping.Ebs = { ...modifiedMapping.Ebs };
+
+      // Only set DeleteOnTermination if it's not already explicitly defined
+      // This respects user's explicit choice if they set it to false
+      if (modifiedMapping.Ebs.DeleteOnTermination === undefined) {
+        modifiedMapping.Ebs.DeleteOnTermination = true;
+      }
+    }
+
+    return modifiedMapping;
+  });
+}
+
 async function createEc2InstanceWithParams(imageId, subnetId, securityGroupId, label, githubRegistrationToken, region) {
   // Region is always specified now, so we can directly use it
   const ec2ClientOptions = { region };
@@ -135,13 +167,14 @@ async function createEc2InstanceWithParams(imageId, subnetId, securityGroupId, l
         Ebs: {
           ...(config.input.ec2VolumeSize !== '' && { VolumeSize: config.input.ec2VolumeSize }),
           ...(config.input.ec2VolumeType !== '' && { VolumeType: config.input.ec2VolumeType }),
+          DeleteOnTermination: true,
         },
       },
     ];
   }
 
   if (config.input.blockDeviceMappings.length > 0) {
-    params.BlockDeviceMappings = config.input.blockDeviceMappings;
+    params.BlockDeviceMappings = ensureDeleteOnTermination(config.input.blockDeviceMappings);
   }
 
   const result = await ec2.send(new RunInstancesCommand(params));