Not yet mentioned, we can make gas and oil from coal reserves or even from biomass. It does make the pool of resources bigger than you think it is.

Those processes cost more than oil/gas extraction does right now. However, if demand was ever high enough, those can be tapped into.

For instance, during WW2 Germany was cut off from oil supplies. But Germany has lots of cheap brown coal, just massive reserves. They built a factory to convert coal -> fuel that was only economical in their wartime economy. That factory was of such important that is was protected by more defenses than Berlin. It has it's own army and airforce just to protect the fuel production.