Guest, no one knows.
Making estimates and forecasts are tricky. Here are a few.
We have used roughly 1000 billion barrels of oil to date. Estimates of proven reserves point to an equal amount remaining.
A major problem with these estimates is that the limits on what is producible shift with advancing technology and exploration.

Canada's 'proven' reserves are second only to Saudi Arabia's (some 300 billion). Using figures like these, there are 885 billion bbls proven reserves in the OPEC nations. This suggests that there is an end coming.
But inserting a large BUT-
1. Looking just at Canada, the Alberta oil sands in total amount to some 1.7 to 2.5 trillion barrels. The problem? Getting them would be very expensive. New technology and higher pricing, however would add tremendously to the 'proven' reserves.
2. Russia, Denmark, Canada and the U. S. are squabbling over boundaries in the Arctic Ocean region. Geologists suspect tremendous reserves in the region, but only drilling will 'prove' how much is there and recoverable.
Britain has hopes for the Malvinas (Falklands) offshore.
The north Pacific reserves north of Sakhalin are only guessed at.
Etc.

3. Other sources of energy.
Some small fleets are beginning to use hydrogen-fueled vehicles (even Santa Fe in New Mexico has a few city vehicles that are hydrogen-fueled).
The mental block against nuclear power is being slowly lifted; this energy source is bound to grow exponentially.

I worked for a major oil company before retirement, in Exploration and Research, so I can make wild guesses too. Mine is that nuclear energy and hydrogen fuels will be developed and important long before fossil fuels give out.

And coal.... Clean technology is achievable for a little more money and regulation.

Gnu- 600 years? I won't argue. I dunno. Other technologies will have advanced, and some reserves may remain always.