The Porter oil field is in southwestern Midland County, close to the center of the Southern Peninsula of Michigan. It was discovered in November, 1931, and since that time has produced more than 39 million barrels of oil. Porter leads all other Michigan fields in total production and in recovery per acre.

All of the oil produced is from Devonian formations; an insignificant percentage of the total production from the Traverse and the balance from Dundee limestone. Accumulation is in the Porter anticline, which is 9 miles long and three miles wide, with a closure of about 50 feet. The productivity of different wells on the anticline varies generally with the percentage of secondary porosity in the uppermost Dundee. This porosity developed mostly during a mid-Devonian emergence.

Deeper drilling in the Porter field to test older formations now productive elsewhere in the Michigan basin is considered desirable.