[Smokin' Joe]

If the temperature is too high, the oil breaks down and you get gas. We have that in the Winnipeg and Deadwood Formations up here in the Williston Basin, too.

Probably the clearest zonation like that happens in the Utica Shale Formation, where there are areas of "dry" gas (mostly methane), "wet" gas (methane with heavier gasses easily liquefied), and where oil and gas are found together.

If the thermal history isn't right, you don't get oil.

[JRandomFreeper]

If the temperature is too high,

I'm going to be willing to bet that isn't a problem on Titan.

/johnny