diff --git a/src/Gateway.php b/src/Gateway.php
index ca1a662..309a4c4 100644
--- a/src/Gateway.php
+++ b/src/Gateway.php
@@ -85,6 +85,25 @@ public function __construct(string $id, string $token, string $environment)
         $this->environment = $environment;
     }
 
+    /**
+     * Pre-authorize a purchase.
+     *
+     * @param array $params
+     *
+     * @return \CraigPaul\Moneris\Response
+     */
+    public function preauth(array $params = [])
+    {
+        $params = array_merge($params, [
+            'type' => 'preauth',
+            'crypt_type' => Crypt::SSL_ENABLED_MERCHANT,
+        ]);
+
+        $transaction = $this->transaction($params);
+
+        return $this->process($transaction);
+    }
+
     /**
      * Make a purchase.
      *
diff --git a/src/Transaction.php b/src/Transaction.php
index 46d7b8a..e202889 100644
--- a/src/Transaction.php
+++ b/src/Transaction.php
@@ -165,6 +165,7 @@ public function valid()
 
         if (isset($params['type'])) {
             switch ($params['type']) {
+                case 'preauth':
                 case 'purchase':
                     $errors[] = Validator::set($params, 'order_id') ? null : 'Order Id not provided.';
                     $errors[] = Validator::set($params, 'pan') ? null : 'Credit card number not provided.';