Petroleum was found in Jurassic strata early in the history of Montana. Part of the oil in the Kevin-Sunburst field reportedly came from the basal Ellis (Sawtooth) sand, the Ellis-Madison contact. This field was discovered in 1921.

Sandstones of the Sundance formations in Wyoming were found to be productive even earlier (1917). No production from Jurassic strata has been found to date in North or South Dakota. A tabulation chart showing present fields producing from Jurassic formations and date of discovery is given. A penetration chart showing depth to Jurassic formations across Montana is included.

Jurassic formations have proved to be productive where suitable reservoir characteristics exist. Changes in facies as well as rapid variance in porosity and permeability should play an important part in pointing future areas to prospect the strata of Jurassic age.

A discussion of the Jurassic of the Sweetgrass area of Montana is reviewed.

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