A barrel of oil: $38 dollars. A quart of oil: $3.99 Whats that about?

So, it must not be my imagination. The price of a barrel, the price OPEC sells it at, has nothing to do with the price of a retail quart by any company selling oil for the engine in your car.

When oil was 150 a barrel, the quart was 3.99, now that oil is 38 a barrel, it hasn't made the oil for my oil changes any cheaper.

Is there something I'm missing about this concept?