THE SEARCH FOR OIL LEES 



235 



the adjacent troughs or synclines. The oil thus concentrated along 

 the summit of such an anticline is actually floating on water within 

 its porous reservoir rock, as illustrated in figure 3, ond if gas is 

 present in greater quantity than can be kept in solution in the oil 

 the excess gas fills the highest part of the anticline, forming what 

 is known as a gas cap. 



The most usual type of oil accumulation is under such anticlinal 

 control. Another type is where the oil is concentrated in the higher 

 edge of a tilted sandstone wedge, and such an occurrence is called 

 a stratigraphic trap or shore-line oil field. Yet further types are 

 where an intrusive body of salt gives a domed structure to the adja- 

 cent strata, or where the sealing of a sandstone layer is caused by 

 a fault. 



Petroleum production (in long tons) 



U.S. A 



U. S. S. R 



Venezuela 



Iran 



Dutch East Indies 

 (British Borneo 



and Sarawak) 



Rumania 



Mexico 



Iraq 



Colombia 



Trinidad 



Argentina 



Peru 



India and Burma 



Bahrein 



Canada 



Germany 



Poland 



Japan and Taiwan._ 



Ecuador 



Egypt 



Albania 



France 



Saudi Arabia 



Hungary 



Other countries 



Total 



In 1938 



167, 705, 000 

 29, 630, 000 

 27, 657, 000 

 10, 192, 000 



8, 194, 



6, 761, 



5, 434, 



4, 298, 



3, 068, 



2, 541, 



2, 386, 



2, 186, 



1, 435, 



1, 117, 



883, 



599, 



541, 



344, 



291, 



222, 



93, 



71, 



66, 



43, 



48, 



000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 

 000 



275, 805, 000 



Percent 

 60.81 

 10.75 

 10.03 

 3.70 



2.97 



2.45 



1.97 



1.56 



1. 11 



.92 



.87 



.79 



.52 



.42 



.32 



.22 



.20 



. 12 



. 11 



.08 



.03 



.03 



.02 



.02 



02 



Total to end 1938 



3, 026, 000, 000 

 575, 000, 000 

 242, 000, 000 

 125, 000, 000 



119,000,000 

 119,000,000 

 271, 000, 000 

 19, 000, 000 

 33, 000, 000 

 23, 000, 000 

 25, 000, 000 



> 137,000,000 



4, 714, 000, 000 



Percent 



64. 19 



12.20 



5. 14 



2.65 



2.52 

 2.52 

 5. 75 

 . 40 

 .70 

 .49 

 .53 



2. 91 



Proved reserves ' 



2, 000, 000, 000 

 700, 000, 000 



1, 580, 000, 000 



80, 000, 000 



4, 360, 000, 000 



' The figures in the last column are the proved reserves on Jan. 1, 1939, estimated by Garfias. 



The oil in its reservoir is under a certain pressure governed by the 

 regional hydrostatic conditions (fig. 3), and it carries gas in solution 

 either saturated to this pressure or some lower pressure, and it is 

 the combination of the hydrostatic pressure and gas content which 

 causes gushers or fountains of oil at the surface. The homely ex- 



