Worldwide supply of oil and natural gas is ultimately linked to the geologic abundance and distribution of those fossil fuels. The U.S. Geological Survey (USGS) has completed a new assessment of the technically recoverable undiscovered oil and gas resources of the world. Nearly 1000 provinces were defined and known petroleum resources exist in 406 of these. A total of 76 priority provinces, containing over 95 percent of the world's known oil and gas, and 52 'boutique', or prospective, provinces were assessed. Based upon our initial analyses, several observations are clear. First, our estimates of total undiscovered technically recoverable petroleum (oil, natural gas, natural gas liquids) resources do not differ greatly (+9.5 percent) from the world totals determined in the 1994 USGS world assessment. However, our estimates of undiscovered oil are up considerably (+24.3 percent), and the regional distribution differs significantly from previous estimates. Secondly, estimates of global undiscovered natural gas resources are smaller than previously estimated (-10.4 percent), largely due to reduced estimates for the former Soviet Union, and natural gas liquids resources are significantly larger than previous estimates because co-product ratio calculations were included in this assessment. In addition, mean estimates of field growth of known oil and gas fields will likely approximate quantities of undiscovered resources and are a critical component of any analysis of world oil and gas supply.