无法使用PHP连接到oracle

I've searched everywhere in google for a solution but I'm still unable to connect to oracle using PHP.

I have the following in my php file

$conn = oci_connect("username","password", "sid");

However, when ever I try and access the php page, I am getting the same error

Fatal error: Call to undefined function oci_connect() in C:\xampp\htdocs\consult.php on line 5.

In XAMPP folders I've looked at the php.ini file and removed the leading semicolon so that I'm left with extension=php_oci8_11g.dll.

I restarted XAMPP, and I'm getting oci8.dll doesn't exist. I then downloaded oracle instant client but I'm slightly confused as to which folder it is supposed to be placed in.