One of the main causes of the recent increases in the indicated reserve is the revision brought about by the increased efficiencies of improved technique and controlled or delayed production. The size of the proven reserve gives no clue to, and logically cannot be expected to reveal, the imminence or remoteness of scarcity. The proven reserve, so estimated, is merely an estimate of the working stock of petroleum in advance of production, which is quite a different matter from the volume of oil yet to be discovered and to be recovered as additional oil from known deposits by improved methods. The only basis for anticipating an ultimate shortage of United States petroleum is a line of reason ing based on the principle of elimination—that each pool found means one less to be discovered in the future—but the sheer magnitude of the proven reserve sheds little light on the ques tions: How much oil is yet to be found? and, To what extent will recoveries be increased by improved technique? The committee of geologists and engineers which made the es timates of reserves for the American Petroleum Institute report : "Large areas within the United States, underlain by sedimentary rocks, are only partly explored for oil reserves, whereas the areas already explored by the best current methods are relatively small. No satisfactory method has been found for assigning a numerical estimate to the amount of oil recoverable from undiscovered deposits. The oil to be discovered in the future is so concealed
from observation that an estimate of ultimate reserves in terms of barrels is obviously impracticable. However, we do have a definite, although incomplete, knowledge concerning the existence in an important part of these slightly explored areas of extensive deformation in sedimentary rocks which are productive in neigh bouring districts, of deeper prospects. . . . This gives reason to expect that ample discoveries will be made to meet national requirements for a period of indeterminate length." Reference also was made to the possibilities of stratigraphic geology. In the past most oil discoveries have been based on the anticlinal theory. The development of the East Texas oil field brought stratigraphic possibilities into prominence. An entirely new field of geology has opened up as a result—the study of flank sands, regional inconformities and up-dip wedging of porosity as possible oil reservoirs. The president of the American Association of Petroleum Geologists, A. I. Leverson, stated in 1936 that there were yet to be discovered oil and gas reserves almost without limit by those who may become adept in stratigraphic analysis, and that, differing from past methods, the possibilities for strati graphic production could not be quickly exhausted. (L. M. F.)