To the best of my recollection, oil is lighter than water, especially lighter than salt water. Why would any oil sink to the bottom?
Because Crude is made up of ‘fractions’ that separate. Some fractions float, some sublimate off the water when they surface, some sink and coat the bottom of the seafloor.
If you do some Googling, you’ll find examples of divers having to go down with ‘vacuums’ to pull pools of oil off the seafloor on spills near docks, in harbors, etc.
Nasty business when you consider the pressure and low temp on the bottom of the seafloor of the gulf.
—the volatile stuff evaporated and the heavy asphalt-like stuff sinks, somewhat similar to what has been going on for millions of years-—tar washes up on the California coast, etc.,-—
API index......
It will sink to the bottom, roll around and mix with sand, basically becoming a lump of asphalt.
Been doing that for thousands of years from natural seepage.