Oil and water samples were collected and analyzed from five fields in West Texas and New Mexico. Two of the fields, Harper and Midland Farms, were "protected"; i.e., the producing formations are not connected by known faults or unconformities and the oils from separate formations are different. Both protected fields are uncomplicated anticlinal traps.

Oil samples from Harper field from the Ellenburger (Lower Ordovician), Devonian, Pennsylvanian, and San Andres (upper Permian) are distinct. Simpson (Lower Ordovician) oil is identical with Ellenburger oil, showing a common source or migration via small faults.

At Midland Farms, Ellenburger and San Andres oils are distinct. Devonian and Silurian oils are similar to each other, because of a similar source, but are different from other oils. Pennsylvanian and Wolfcamp (lower Permian) oils also are similar to each other for the same reason, but are different from other oils.

Justis and Embar fields are "unprotected"; i.e., some of the producing formations are connected by faults or unconformities and the oils in the different formations are similar. In both fields lower Permian rocks overlie lower Paleozoic strata unconformably. Both fields are faulted on the east flank.

At Justis, Ellenburger and Simpson oils are similar but not identical, possibly due to mixing from two sources. Montoya (Upper Ordovician), Silurian, and Clearfork (Leonard-Permian) oils are almost identical. This similarity may be due to a common source. It may also be due to migration, via faults, from pre-existing Montoya-Fusselman pools to the Clearfork. Seven Rivers-Queen (upper Permian) oils are different from others in the field.

At Embar there are several transverse faults. At Block 11 field, 2 mi west of Embar, lower Permian rocks overlie the Devonian. The Devonian is absent on the crest of Embar, but is present and productive in downthrown blocks on the east flank. Ellenburger, Silurian, Devonian, and Clearfork oils at Embar are very similar due to migration from a common source or to migration via faults. Devonian oils at Block 11 are similar to but slightly different from oils at Embar.

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