We had black oily crap in the rain in Florida back in the late 1980s. It was basically a wet sooty material that had drifted over from Mexico and was dumping in the rain in Florida. The stuff would form under just the right (some would say wrong) conditions in the atmosphere and bind with other substances although it was more like ash than oil when it hit.

Extreme weather out in the gulf can cause evaporation so hard and so fast, and waterspouts so strong that it is not entirely unheard of for small fish to come plopping down with the rain in some areas.