The first theory is, chances are, the one you're familiar with: oil is a fossil fuel. Al Gore particularly likes that theory, as does the Left, since it's how they can drum up support (hey, it's a living) for decreased oil consumption. Don't use it all up, kids, 'cause in 50 years it's all gone.
Producing a new aristocracy in the interim... which is what the Bu$hies are into. Which likely means Cheneyburton believes it, as well. Some kinda NeoLiberals, those.
The other theory is the "abiotic" theory which the Russians and many of the Right wingnuts seem to favor saying that oil is continually produced by geochemical processes. Or God. Or somehow.
Which none of their leaders may believe, since it means there would be no way they could ever hope to establish their hegemony.
It may be that's the horn they toot because they want you to drive faster and use up all the oil.
Then there's the other theory, which is circumstantial, unsupported by any research, and of course, my pet crackpot idea. It has to do with methane clathyrates. These are found naturally- trillions of tons worth- at the bottom of bodies of water like the Gulf of Mexico. They are also found (in uncomfortably high concentrations) associated with the oil that's found in the sediments at the Gulf of Mexico and other places.
These are produced by methanogenic bacteria in chemical reactions similar to the ones in your own gut. At high pressures and cool temperatures, however, the methane instead of being a gas, forms a semisolid gel with water. My bet- which nobody's officially ever tried to examine to my knowledge- is that under the floor of the ocean's sediments some extremophilic bacteria manage to glean some energy to survive by turning that methane into long-chain hydrocarbons. Like gasoline.
Of course, the idea that gasoline really is a renewable resource if you couple together the right enzymes to make it is an idea guys like Craig Venter cherish. That there may be metric tons of these organisms spewing up- and likely dying in the process- from the Gulf floor right now is one that does not seem to occur to anyone.
The idea that by culturing said organisms, or cloning their genes into bugs we can grow in the lab, we might be able to halt all drilling everywhere and end some very lucrative wars in the process does not seem to occur to polite company.
Just to be perfectly clear, I imagine that biogenic not abiotic oil is renewable, but to get a reservoir the size of Saudi Arabia's or the Gulf of Mexico's it's still probably going to millions of years. That's a guestimate.
So yes, I think we probably will use it all up, but I also think the biology is out there to support a biotechnological industrial base.
I think it's also a safe bet those who would rule us won't allow its development until they've squeezed every last cent out of the ground.