Crude oil is a green product
There is only one problem in that it takes time for it to self-destruct and during that time animals and vegetation will ingest the toxins and perish.
Refineries turn crude into a totally non-green product by pasteurizing the crude (killing the microbes that will eat up the oil) and create many different sterile hydro- carbon products.
When refined hydrocarbons are poured on the ground or disposed of in an improper fashion the oil coats the soil and renders the microbes attached to that soil useless. The oil continues to migrate as it travels with ground water, eventually gets below the oxygen level in the soil.
At this level no break down will occur and the oil continues its journey to the water table and contaminated it