Eric,
The earth works in a fashion similar to a petroleum distillation column at an oil refinery. The heavy stuff is at the bottom. The light stuff is as the top.
However, the crust of the earth is not uniform. Hydrocarbons created in one place may migrate into hydrocarbons created in another place.
Also, in the crust of the Earth, you have additional factors working, e.g., magma flows. Sulfur gets mixed in and the resulting crude oil is no longer “sweet crude” oil.
I began my energy career in coal.
It definitely is a fossil derived product.