Under a cooperative agreement between the Bureau of Mines Oil-Shale Demonstration Branch and the Denver & Rio Grande Western Railroad Co., the Bureau supplied the railroad with 5,000 gallons of Diesel fuel produced at Rifle from oil shale to be used for a 5-week operational test on one of the railroad's Diesel switch engines. This fuel, representing 22.5 percent of the crude shale oil, gave satisfactory performance in all respects. Inspection of the engine at the conclusion of the test showed no unusual difficulties developing, and the parts were in good condition comparable to similar periods on petroleum fuel. Longer test periods will be necessary to determine what difficulties, if any, may result from the use of shale Diesel fuel.