Estimating the total petroleum resource has been an ongoing endeavor of the oil companies as well as of government agencies such as the US Geological Survey(USGs) Table 2.1 estimates of undiscovered recoverable oil and natural gas in the us Natural Gas (Billion Barrels) (Trillion Cubic Feet) Oil Companies Company A(Weeks, 1960) l68 Company B(Hubbert, 1967)a 2164 280-500 Company C(1973)b Company D(1974) 89 450 U.S. Geological Survey Hendricks(1965) 346 1300 Theobald et al. (1972) 1980 McKelvey (1974) 200400 990-2000 Hubbert(1974) UsGS(1975) 61-149 322-655 UsGs(1989) 399 USGS(1995) 93 939 National Academy of Sciences National Research Council (1975) 113 U.SEnergy Information Admin.(105Estimating the total petroleum resource has been an ongoing endeavor of the oil companies as well as of government agencies such as the US Geological Survey (USGS). Table 2.1 Estimates of Undiscovered Recoverable Oil and Natural Gas in the US. Oil (Billion Barrels) Natural Gas (Trillion Cubic Feet)