482 



UNITED STATES MINERAL RESOURCES 



tributed according to the age of the reservoir rocks. 

 Their data (fig. 58) show 29 percent to be Cenozoic 

 (0-74 m.y.b.p. (million years before present)), 57 

 percent to be Mesozoic (74-200 m.y.b.p.), 8 percent 

 to be Permian (200-225 m.y.b.p.), and less than 6 

 percent to be pre-Permian in age. For comparison, 

 Radchenko (1968, table 50) gives, on the basis of 

 "data up to 1960," 49.4, 21.5, 4.7, and 24.4, respec- 

 tively, as the percentages of total w^orld cumulative 

 production for the same four stratigraphic intervals. 

 Current estimates for the United States yield per- 

 centages that are significantly diff'erent from either 

 set of world percentages (fig. 58). The percentages 

 of known producible hydrocarbons from U.S. reser- 



voir rocks of both Cenozoic and Paleozoic ages are 

 much higher than the world percentages, and that 

 for Mesozoic reservoirs are much lower. These dif- 

 ferences reflect the strong influence of the vast 

 reserves in the Middle East (more than 62 percent 

 of the world reserves), a large part of which are in 

 reservoirs of Mesozoic age. Considering only pro- 

 duction and reserves from "giant" fields outside the 

 Persian Gulf region. Tertiary, Mesozoic, and Paleo- 

 zoic rocks contain 40, 39, and 21 percent, respec- 

 tively, of the total producible reserves. As off'shore 

 exploration and development in the United States 

 continue, the U.S. percentages for Cenozoic and 

 Mesozoic hydrocarbons will doubtless increase at 







5y 



United States 

 (15 percent of world total) 



"~r" 



200 



1 — r 



RADIOMETRIC AGE 

 (MILLIONS OF YEARS BEFORE PRESENT) 



Figure 58. — Age-dependent variations in produced and proven reserves of oil and gas for the United States and the world. 



