is there any reliable information, or even a half-decent ball park estimate, on how much oil there is left in the world?

I understand that we know where some oil is and how much it will cost to extract. (Reserves)

I also know we have some idea where there is more oil available, that will be extractable if prices go up, or technology improves. (Recoverable)

And there is probably some oil out there just waiting to be found but we have no idea where it is and no way to guess...yet. (Undiscovered)

When I worked at Gulf Research Labs in the early 1980s none of the Texas cowboys there could (or would) answer that question. They either gave totally contradictory answers, or they changed the subject. Does anyone really know? And if they know, are they talking? Are there even trustworthy guesses by people who don't have axes to grind?

If they're all lying, I trust you could probably give at least an order-of-magnitude estimate, broken down by those 3 categories.

How much time have we got?