The Deep River oil field is north and east of the Deep River gas field in west-central Arenac County, Michigan, about 44 miles north of Saginaw. The discovery well was completed at the close of 1943 and development had practically ceased by the end of 1946. The field is decidedly elongate, with a northwest-southeast trend. The producing zone is a streak of porous dolomite surrounded by impervious limestone. It lies at the top of the Rogers City formation of Devonian age. The depth to the reservoir averages about 2,800 feet. The Deep River oil field is on the north and northeast flanks of a broad dome. The gas field, producing from Berea sandstone of Mississippian age, occupies the highest parts of the dome. The Rogers City formation is "tight" limestone where tested near he top of the dome. It is suggested that excess of solution over precipitation by dolomitizing solutions rising through a fracture in the Rogers City limestone produced the porosity resulting in the accumulation of oil in the Deep River oil field. Initial productions ranged up to 7,000 barrels. The yield for 1946 was nearly 2 1/2 million barrels, from 100 wells. At that time the recovery per acre was 4,605 barrels.