ENERGY FROM FOSSIL FUELS — HUBBERT 263 



AMOUNTS OF FOSSIL FUELS 



Although the quantities of fuels upon the earth are not known pre- 

 cisely, their order of magnitude is pretty definitely circumscribed. 

 The most accurately known is coal. At the Twelfth International 

 Geological Congress at Ottawa in 1913 a world review of coal was 

 made and the amount capable of being mined was estimated to be 

 about 8 X 10^- metric tons. Since that time some adjustments in the 

 estimates have been made, giving us a present figure of about 6.3 X 10^^ 

 metric tons of coal initially present. 



Within the past few years this figure has been criticized by mining 

 engineers (8, 9) on the grounds that while the estimated amount of 

 coal may in fact be present, the amount recoverable by practical min- 

 ing operations is but a fraction— possibly as small as one-tenth — of 

 the foregoing estimate. The degree of validity of this criticism still 

 remains to be determined. 



For petroleum the accuracy of estimation is considerably less than 

 for coal but still is probably reliable as to the order of magnitude. 

 The method of estimation in this case is that of sampling. In the 

 better-known areas the amount of petroleum produced per unit vol- 

 ume of certain classes of rocks has been determined. The areas and 

 volumes (within drillable depths) of similar rocks over the earth are 

 fairly well known. By application of the same factor for the un- 

 drilled areas as for those now well known, an order of magnitude of 

 the petroleum that may exist may be obtained. 



The most comprehensive of such studies that have so far been made 

 public appear to be those of Weeks, which are cited by Wallace E. 

 Pratt (10, 11, 12). According to these studies, in a volume of 

 10-12.5 X10« kilometers^ (2.5-3.0X10*' miles^) of sediments in the 

 United States there have already been discovered 8.4 X lO'' cubic meters 

 (53X10^* barrels) of oil. This represents about 10 percent of the 

 total volume of such sediments of the land areas throughout the 

 world. Hence, it is estimated that for the world there should have 

 been present initially the order of 10 times as much oil as for the 

 United States. A similar volume of sediments occurs on the conti- 

 nental shelves which may contain a volume of oil about equal to that 

 of the land sediments. 



Assuming that the land areas of the United States will produce 

 16X10^ cubic meters (100 billion barrels), then a reasonable estimate 

 for the world would be : 



Land 160Xl(ym.* 



Continental shelves 160X10°m.' 



Total 320X10'm.' 



922758—51 18 



