The Tuxedni-Hemlock(!) petroleum system, situated in the Cook Inlet area in southern Alaska, originally contained discovered recoverable hydrocarbons of about 1.18 billion bbl of oil and 2.48 trillion ft³ of gas. This system, which covers 2200 km², encompasses six commercial oil fields in the Cook Inlet area. Sedimentary rocks of the system, which range in age from Middle Jurassic to Holocene, were deposited in volcanic forearc and backarc basins adjacent to a convergent margin. Carbon isotope and biological marker data indicate that the low sulfur, 28°-42° API gravity oil originated from the source rock in the Middle Jurassic Tuxedni Group. Burial and thermal history reconstructions indicate that the oil was generated and migrated from below the Cenozoic depocenter between the Middle Ground Shoal and Swanson River oil fields during Cenozoic time. Here, the overburden rock is 9.8 km thick and ranges in age from Late Jurassic to Holocene. The principal reservoir rock is the Hemlock Conglomerate of Oligocene age. Traps are anticlines that are commonly faulted and sealed by siltstone; these traps, which are still evolving, started to form during late Cenozoic time.

The essential elements of the petroleum system (source, reservoir, seal, and overburden rocks) were deposited from Middle Jurassic (~170 Ma) to the present. The petroleum system processes (generation-migration-accumulation and trap formation) began in the Paleocene (~63 Ma) and continue to the present.

The quantity of hydrocarbons generated by the Middle Jurassic source rock was calculated and compared to the estimated in-place petroleum to determine the generation-accumulation efficiency of the petroleum system. On the basis of the average organic carbon content (1.7 wt. %), the difference between the original and present-day hydrogen indices (200 mg H/g OC), and the volume of mature source rock (1.5 10¹⁸ cm³), 134 10¹¹ kg hydrocarbons were generated. In-place hydrocarbons are estimated at 5.3 10¹¹ kg. On the basis of these calculations, 4% of he hydrocarbons generated actually accumulated in discovered traps.