Billy Creek anticline is a closed fold on the west side of the Powder River syncline. The producing sand is exposed about 3 miles west of the field, where it is upturned along the Big Horn Mountain front. The gas-producing sand belongs to the Frontier formation, and by some is regarded as equivalent in age to the First “Wall Creek” sand at Salt Creek. Subsurface structure does not conform exactly to surface structure, the axis of the fold is inclined toward the mountains. The anticline has been tested by 11 wells, and the gas area is considered fully developed. A unit operation plan is being worked out to control and regulate future drilling and insure economic operations.