This is how. link below.
"...while the world's proved (1P) reserves of oil have been on an apparent ever-upward path according to the main suppliers of this information (including national reporting agencies) and now stand at up to 1700 Gb or so, our adjusted oil-industry data for global proved-plus-probable (2P) oil reserves reached a peak around 1985, and have been in steady decline since. Thus, we suggest that the global reserves of ‘realistically-accessible’ oil (essentially, conventional oil including ‘light-tight’ oil) are probably only about 750 Gb or so, once the extra heavy oils and adjustments for probable overstatements of Middle East and FSU reserves have been subtracted. Moreover, this measure of oil reserves has been on a declining trend for over 35 years, and would last only about 25 years at current rates of production."
"..our findings suggest that unless the world rapidly weans itself off oil for reasons of climate change, there are likely to be significant economic and political consequences due to oil resource limits, as first conventional oil, and then all-oil, become supply-constrained. "
