Abstract. The Ultimate Resources of world petroleum are assessed in about the same quantities and distributed broadly in the same areas as was reported to the Ilth World Petroleum Congress. The assessment as of 1/1/85, for the 12th World Petroleum Congress is: Oil (BBO) Gas (TCF) NGL (BB) Cumulative production 524 1173 Undiscovered resources Identified reserves 795 3908 59 95% 262 2650 Mode 425 4199 63 5 %o 927 8591 Ultimate resources 1744 9280 Two of the component parts of the assessment of Ultimate Resources of crude oil-the Original Reserves and the Undiscovered Resources-were compensatingly altered in this assessment by about 150 billion barrels (24 Gm3); the Original Reserves were increased and the Undiscovered Resources decreased. The reserves change reflects, heretofore uncounted, additions to reserves owing primarily to concepts of field growth. Including the field growth projections, it appears that world discovery over the past decade has been slightly less than production. The change in Undiscovered Resources derives in large part from a clearer understanding of the geologic limits to resource occurrence in the USSR and in Mexico, and from exploration failures in several key areas in the United States. Though the natural gas assessment remains substantially the same, there appears to be evidence of substantial under-reporting of gas resources owing to market immaturity. Assessments of heavy and extra-heavy crude oils, natural bitumens, and shale oil from oil shale remain reasonably consistent with past reports but economic reserves of these unconventional resources have increased owing to the expansion of commercial recovery projects.
The distribution of conventional oil and gas is very strongly concentrated in the Eastern hemisphere while the world's unconventional resources are most prominent in the Western Hemisphere-notably in Venezuela and in Canada. Though ultimately only 25% of the world's oil will have been discovered offshore, 45% of the remaining Undiscovered Resource is assessed to be offshore. Natural gas also remains highly imbalanced in its distribution and, in addition, its production is imbalanced relative to the reserves distribution; the Middle East gas reserves are one of the largest underutilized energy resources in the world. Undiscovered Resources of gas are mainly concentrated in areas of large Original Reserves but assessed occurrences in the frontier Barents Sea likely will exceed 300 TCF (8.5 Tm3) and in the Niger delt