Even just looking at oil reserves, it’s not known how much there is. The numbers change as new speculative oil reserves become proven or disproven. And also, there are different conditions for extraction – there are easier/safer oil fields to extract from (e.g. Texas & California) and more dangerous/expensive/dirty ones we hopefully won’t ever fully eploit (e.g. Tar Sands, Arctic).
But to take one stab, one report indicates that the total world reserves of crude oil including lease condensate reserves, at some point in 2020, was 1662 billion barrels. Another site with a handy calculator estimates 35.4 billion barrels used per year, and estimates 47 years at that rate.
Note that that is actually also consistent with a 100-year estimate, IF we assume that humans attempt to reach 0% usage by the time the fuel runs out. A theoretical steady abandonment of fossil fuels would tend to double the time it takes to use it up. But that’s a crude way of estimating such a complex situation.