>https://www.nytimes.com/1995/09/26/science/geochemist-says-oil-fieldsmay-be-refilled-naturally.html?pagewanted=all&src=pm
called "abiogenic" oil meaning it's produced by processes other than biology
not decaying organic matter but rather the chemical synthesis of hydrocarbons from materials in the Earth's mantle due to heat & pressure.
FYI you can use an archive service to get past a paywall
http://archive.md/lDg1C