This is the result of high pressures, water, extreme heat, methane and carbon dioxide, cooking deep underground. This oil seeps up everywhere, but certain sedimentary geologic formations trap it. These also contaminate the oil, based on whatever other organic sludge was there. Various bacteria actually thrive on these hydrocarbons, and break them down quickly into water vapor and carbon dioxide, if these molecules aren't trapped underground. (The same bacteria that eats oil spills. Spills just overwhelm them, and it takes a while to break a spill down.)
The Russians can't be wrong about everything. Could it be that the dinosaur aged swamp is contaminating the oil? I just offer it as an alternate idea. No tinfoil hat.
Sounds plausable to me, I’ve thought for years, well before reading anyone else say that the earth manufactures oil constantly.
They have even found areas where the oil was pumped dry years ago now contain more oil.