The conditions causing the commercial occurrence of oil and gas in the recently discovered fields of the Pettus district, Bee County, Texas, show a striking similarity to those surrounding the older and better known fields of the Mirando district, 100 miles farther southwest. The productive sands in both districts are confined to a stratigraphic section, limited by basal Frio sediments above and by middle Yegua sediments below, which is mainly of Fayette age.

In the Mirando district, accumulation has occurred in narrow strike lenses, formed under conditions of shore-line deposition, in which gradations in porosity have formed traps. Source material, from which the oil and gas were derived, was deposited within, or adjacent to, the present producing horizons. True deformation is ordinarily absent, although folding or fracturing may, in some places, have exerted a minor influence.

Present knowledge of conditions at Pettus indicates that the same factors were primarily the cause of the oil and gas segregation in this area. In the Pettus field proper, accumulation occurs within a lensing sand which follows a definite strike trend. There is no evidence of positive structural influence.

The conclusion is reached that, within the upper Eocene section throughout the inner margin of the Gulf Coastal Plain, strata of basal Frio, Fayette, and upper Yegua age contain differences in porosity sufficient to trap oil and gas, in the absence of structural influence. The following of established strike trends will prove the most effective means of locating such pools.