Middle Ground Shoal oil field is in the Anchorage basin, Alaska, 21 miles west of Swanson River oil field, about 52 miles west-southwest of Anchorage, and is located centrally in Cook Inlet just north of the restriction formed by the East and West forelands. It was discovered by the Shell-Richfield-Standard group drilling from a floating vessel in the summer of 1963. This was about 4 years after the first marine reflection-seismic survey was conducted in Cook Inlet by an 11-company group, and almost 6 years after the discovery of Alaska's first major oil field, Swanson River.

Cook Inlet is probably one of the most difficult marine areas in the world in which to look for and develop oil reserves. Conditions, such as 25-35-foot tides, 6-8-knot tidal currents, strong winds, and pack ice make all phases of the operation extremely hazardous and tax the ingenuity of the men involved. A motion picture of the platform construction portrays this aspect.

First production was accomplished late in 1965 when the valve on the 7-mile pipeline to shore was opened. At the present time, operations are being conducted from two permanent platforms; a third will be constructed in 1966; and others may follow.

As the early phases of development are begun, the Middle Ground Shoal accumulation appears to be trapped by a very tightly folded north-south trending anticline. It is bounded along the west side by a major fault with a throw of 10,000 feet or more. In gross aspect, this anticline is near the western side of a long, narrow, non-marine Tertiary basin where vertical tectonics appear to be dominant.

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