diff --git a/src/Service/ExchangeRatesApi.php b/src/Service/ExchangeRatesApi.php
index 9683ebb..4b44a6b 100755
--- a/src/Service/ExchangeRatesApi.php
+++ b/src/Service/ExchangeRatesApi.php
@@ -31,9 +31,26 @@ final class ExchangeRatesApi extends HttpService
 {
     use SupportsHistoricalQueries;
 
-    const LATEST_URL = 'https://api.exchangeratesapi.io/latest?base=%s';
+    const LATEST_URL = 'https://api.exchangeratesapi.io/latest?base=%s&access_key=%s';
+
+    const HISTORICAL_URL = 'https://api.exchangeratesapi.io/%s?base=%s&access_key=%s';
+
+    const ACCESS_KEY_OPTION = 'access_key';
+
+    /**
+     * {@inheritdoc}
+     */
+    public function processOptions(array &$options): void
+    {
+        if (!isset($options[self::ACCESS_KEY_OPTION])) {
+            throw new \InvalidArgumentException('The "access_key" option must be provided to use exchangeratesapi.io');
+        }
+
+        if (!isset($options['enterprise'])) {
+            $options['enterprise'] = false;
+        }
+    }
 
-    const HISTORICAL_URL = 'https://api.exchangeratesapi.io/%s?base=%s';
 
     /**
      * {@inheritdoc}
@@ -44,7 +61,8 @@ protected function getLatestExchangeRate(ExchangeRateQuery $exchangeQuery): Exch
 
         $url = sprintf(
             self::LATEST_URL,
-            $currencyPair->getBaseCurrency()
+            $currencyPair->getBaseCurrency(),
+            $this->options[self::ACCESS_KEY_OPTION]
         );
 
         return $this->doCreateRate($url, $currencyPair);
@@ -60,7 +78,8 @@ protected function getHistoricalExchangeRate(HistoricalExchangeRateQuery $exchan
         $url = sprintf(
             self::HISTORICAL_URL,
             $exchangeQuery->getDate()->format('Y-m-d'),
-            $exchangeQuery->getCurrencyPair()->getBaseCurrency()
+            $exchangeQuery->getCurrencyPair()->getBaseCurrency(),
+            $this->options[self::ACCESS_KEY_OPTION]
         );
 
         return $this->doCreateRate($url, $currencyPair);
diff --git a/tests/Tests/Service/ExchangeRatesApiTest.php b/tests/Tests/Service/ExchangeRatesApiTest.php
index 2dbcaa1..0310a77 100644
--- a/tests/Tests/Service/ExchangeRatesApiTest.php
+++ b/tests/Tests/Service/ExchangeRatesApiTest.php
@@ -29,7 +29,7 @@ class ExchangeRatesApiTest extends ServiceTestCase
      */
     public function it_does_support_all_queries()
     {
-        $service = new ExchangeRatesApi($this->createMock('Http\Client\HttpClient'));
+        $service = new ExchangeRatesApi($this->createMock('Http\Client\HttpClient'), null,  ['access_key' => 'x']);
 
         $this->assertTrue($service->supportQuery(new ExchangeRateQuery(CurrencyPair::createFromString('USD/EUR'))));
     }
@@ -39,7 +39,7 @@ public function it_does_support_all_queries()
      */
     public function it_supports_eur_base()
     {
-        $service = new ExchangeRatesApi($this->createMock('Http\Client\HttpClient'));
+        $service = new ExchangeRatesApi($this->createMock('Http\Client\HttpClient'), null, ['access_key' => 'x']);
         $this->assertTrue($service->supportQuery(new ExchangeRateQuery(CurrencyPair::createFromString('EUR/CAD'))));
     }
 
@@ -48,7 +48,7 @@ public function it_supports_eur_base()
      */
     public function it_does_support_other_than_eur()
     {
-        $service = new ExchangeRatesApi($this->createMock('Http\Client\HttpClient'));
+        $service = new ExchangeRatesApi($this->createMock('Http\Client\HttpClient'), null, ['access_key' => 'x']);
         $this->assertTrue($service->supportQuery(new ExchangeRateQuery(CurrencyPair::createFromString('USD/CAD'))));
     }
 
@@ -60,10 +60,10 @@ public function it_throws_an_exception_with_error_response()
         $this->expectException(Exception::class);
         $this->expectExceptionMessage('Base \'FOO\' is not supported.');
 
-        $uri = 'https://api.exchangeratesapi.io/latest?base=FOO';
+        $uri = 'https://api.exchangeratesapi.io/latest?base=FOO&access_key=x';
         $content = file_get_contents(__DIR__.'/../../Fixtures/Service/ExchangeRatesApi/error.json');
 
-        $service = new ExchangeRatesApi($this->getHttpAdapterMock($uri, $content));
+        $service = new ExchangeRatesApi($this->getHttpAdapterMock($uri, $content), null, ['access_key' => 'x']);
         $service->getExchangeRate(new ExchangeRateQuery(CurrencyPair::createFromString('FOO/EUR')));
     }
 
@@ -73,10 +73,10 @@ public function it_throws_an_exception_with_error_response()
     public function it_fetches_a_rate()
     {
         $pair = CurrencyPair::createFromString('EUR/CHF');
-        $uri = 'https://api.exchangeratesapi.io/latest?base=EUR';
+        $uri = 'https://api.exchangeratesapi.io/latest?base=EUR&access_key=x';
         $content = file_get_contents(__DIR__.'/../../Fixtures/Service/ExchangeRatesApi/latest.json');
 
-        $service = new ExchangeRatesApi($this->getHttpAdapterMock($uri, $content));
+        $service = new ExchangeRatesApi($this->getHttpAdapterMock($uri, $content), null, ['access_key' => 'x']);
         $rate = $service->getExchangeRate(new ExchangeRateQuery($pair));
 
         $this->assertEquals(1.0933, $rate->getValue());
@@ -91,11 +91,11 @@ public function it_fetches_a_rate()
     public function it_fetches_a_historical_rate()
     {
         $pair = CurrencyPair::createFromString('EUR/AUD');
-        $uri = 'https://api.exchangeratesapi.io/2000-01-03?base=EUR';
+        $uri = 'https://api.exchangeratesapi.io/2000-01-03?base=EUR&access_key=x';
         $content = file_get_contents(__DIR__.'/../../Fixtures/Service/ExchangeRatesApi/historical.json');
         $date = new \DateTime('2000-01-03');
 
-        $service = new ExchangeRatesApi($this->getHttpAdapterMock($uri, $content));
+        $service = new ExchangeRatesApi($this->getHttpAdapterMock($uri, $content), null, ['access_key' => 'x']);
         $rate = $service->getExchangeRate(new HistoricalExchangeRateQuery($pair, $date));
 
         $this->assertEquals(1.5209, $rate->getValue());
@@ -109,7 +109,7 @@ public function it_fetches_a_historical_rate()
      */
     public function it_has_a_name()
     {
-        $service = new ExchangeRatesApi($this->createMock('Http\Client\HttpClient'));
+        $service = new ExchangeRatesApi($this->createMock('Http\Client\HttpClient'), null, ['access_key' => 'x']);
 
         $this->assertSame('exchange_rates_api', $service->getName());
     }