This is a complex question, because the quality of the oil matters as well. We’ve gotten the good stuff, the light, easy oil, and a lot of the remaining oil will take a lot more energy and complex refineries to process.
The Association for the Study of Peak Oil has been studying this for over a decade and has many country-by-country reports.
Robert Rapier. Jun 25, 2012. How Much Oil Does the World Produce?
Cornucopians keep coming up with rosy predictions. This article: Don’t worry, be happy, there’s plenty of oil, natural gas, & coal left has a list of articles that rebut their arguments, good summaries of how much oil is left and why peak oil is nearly upon us.
Robert Hirsch estimates oil shortages will begin roughly 2012-2015 and that even a worldwide depression won’t affect that time-frame by more than a few weeks.