You also gotta realize just how fucking massive the oil transport operation is. There are an estimated SIX THOUSAND tankers of various types in the world, and I bet they run damn near non-stop. Oil is the worlds blood, "the oil must flow!" isn't just a rip off a sci-fi book. No one has the capability to police all of them and quite frankly, everyone has all the incentives (aka $$$) in the world to NOT look too closely at how the blood shows up, so long as it keeps coming.