A multiple drill carriage or "jumbo," which is believed to be unique in both design and performance, was constructed and has been in use for the past year at the Bureau of Mines experimental oil shale mine near Rifle, Colorado. This jumbo mounts four long feed percussion drills and is so designed that two men can operate all four drills. Before the jumbo was placed in operation, a minimum of eight man shifts was required to drill 72 fifteen foot holes in headings 60 feet wide and 27 feet high. The same round is now drilled by two men in about 6 hours. Over 500 feet of drill per man shift is easily and consistently accomplished. Use of the jumbo has resulted in a 75% reduction in drilling labor and a substantially lower drilling cost.