You can be sore at the oil companies all you want, but they are no different than any other profit making organization including, as you have found out, the biodiesel producers.

Price levels in a free enterprise system are determined by one thing, supply and demand. It stands to reason that if the petroleum based fuel prices increase, the demand for the biodiesel should increase, thus the demand will cause price to increase.

That's about as simple as you can boil down the economics of commodity pricing.

Best of luck,