Eye candy? Yes, who can resist those chipmunk cheeks of McCain! A sure winner with that phiz.
(haw!)
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Donuel, you are largely correct. Predominantly single-celled plant and animal critters, microscopic in size. Also pollen, some plant and marine animal tissues, etc. that wash into an anoxic where organics can be presrvedenvironment.

The stuff must be buried and subjected to moderate heat and pressure to convert the organic materials into hydrocarbons and express the hydrocarbons and move them to reservoir (porous) rocks from which they can be pumped out. Too much heat and pressuse and the liquid hydrocarbons are converted into dry gas, and in the end, lost.
The oil shales and sands are an example of where the hydrocarbons have formed but have not been expressed into reservoir rock, thus must be mined and treated to get the product free of the clay, sand, etc. in which they are bound. Takes a lot of water and tears up the landscape (e. g., the 'tar sands' of Alberta).

Still lots left, and new deposits are found with new techniques, but nuclear, geothermal, hydrogen generation, wind and solar are all much less contaminating to the environment. Some energy companies (e. g. Shell) have mounted extensive research programs.