Using new vegetable oil -- not the used stuff from restaurants -- raises similar scarcity questions.

CNN: Can vegetable-oil cars save the world?

But much of that dip appears to be the result of microbes using oxygen to dissolve oil underwater, and the decline is not enough to be fatal to marine life, said National Oceanic and Atmospheric Administration official Steve Murawski, the head the Joint Analysis Group studying the spill's impact.

CNN: No signs of 'dead zone' in Gulf, feds say

Refiners churn out the same end products (gasoline, heating oil, distillates, etc.) using either feedstock, but not all refiners have the equipment to process heavy sour crude.

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