A compressor and utility station, which is believed to be one of the largest mobile units of this type ever constructed, was placed in operation at the Bureau of Mines experimental oil shale mine near Rifle, Colo., during 1949. This mobile unit mounts two 77o cubic feet per minute air compressors, a 2,500 gallon water tank, and a 200 cubic foot air receiver. The mobile base of the unit is a 30 ton trailer 30 feet long and 12 feet wide. Prior to the construction of this unit, compressed air was supplied to underground workings through pipe lines connecting with a stationary compressor plant on the surface. The power consumed in supplying compressed air to underground drilling crews was 0.531 kw-hr per ton of shale broken. Use of the mobile unit has cut this figure to 0.421 kw-hr per ton of shale broken and, more important, has eliminated the cost of installing and maintaining underground air and water lines.