No, that isn't the case at all. For over 70 years we were obtaining Oil from these nations without being tied down to this pact. Purchasing Oil is a simple business transaction that has been taking place for years.
This security pact greatly benefits Saudi, and whilst we're not privy to finer details, on the surface I can't see any tangible benefits for Pakistan. Once again our rulers failed to put our interests first.
You have to remember we are the sole Nuclear power in Islamic world, and we should have obtained an arm and a leg in return for providing this shield. But the question is, did we?