In these days, when detailed investigations of stratigraphy, structure, andsand conditions so frequently result in the discovery of new oil fields, andapplause from oil companies and the public, geologists do well to walk humbly, and punctiliously to admit that the geologic principles controlling thedistribution of oil and gas have as yet been discovered only in part, and thatwhat remains yet to be learned is probably vastly more than what is alreadyknown. The few experiments already attempted have been fragmentary, andsomewhat desultory, and however positive each of us may be with respect tocertain theoretical conclusions, many of the fundamental questions as to theorigin and mode of occurrence of petroleum are subject to radical disagreement.Of the chemical changes attending the generation of petroleum from organicmatter, little is actually known. Most of the postulated formulas are liable tobe misleading, through ignorance of essential factors. Open-mindedness istherefore a prime essential at the present stage of our science. Nevertheless, adopting the hypothesis that oil originates in some manner fundamentallyconnected with the organic theory, and in possible departure from suchopen-mindedness, the writer will pay no attention to the so-called inorganictheory, since every attempt to apply this theory to the study of old oilfields, or to the discovery of new ones, affords cumulative evidence of itsinadequacy. In this paper, some of the factors affecting the occurrence of petroleum thatthe writer believes worthy of consideration by the prospector for oil in anynew region will be discussed. Some of these, which are less generallyunderstood, will be considered somewhat in detail. Other points, thesignificance of which cannot now be determined, require more field study, andfor that reason are here brought to the attention of the field geologist. Onthe other hand, certain theoretical points which do not bear especially on theoil possibilities of a new region will be given little or no attention. Themain topics that will be discussed are:sufficiency of carbonaceousdetritus and residues in the oil-forming rocks;stage of carbonization ofthe organic matter in the oil-bearing formations;folding of the strata;thickness of sedimentary formations;conditions of deposition. AIME 065–21