This is about #2 fuel oil, not gasoline, so I dunno if it's relevant or not.
Years ago I had a job pulling underground fuel tanks to meet the new standards (double walled, corrosion protected, leak detection, etc.)
Some of these were back up fuel for natural gas boilers, and so 10,000 gallons of fuel oil had been sitting for ten years or so. When we pumped that oil, most of it was good. Some had a bit of water especially if the tanks leaked.
A year or two later I had to pull one of the new tanks, I forget why; maybe the building was demolished or something. There was almost a foot of gooey sludge at the bottom, kind of like a soft jello. Our environmental section said it was probably biological growth, that the refinery process had changed and oil was subject to this much faster.