Hydraulic mining of the three thickest seams at Pittsburg & Midway Coal Mining Company's property at Kemmerer, WY, is technically and economically feasible because of the great thickness of the seams (30 to 90 ft), the 20 deg. Pitch, the absence of gas, the self- supporting top coal, and the low ash and sulfur content. Access to the coal seams is by 11,000-ft twin rock tunnels, declining on a 21 deg grade to a central underground dewatering station where the plus 14-mesh coal is screened off and conveyed out. The minus 14-mesh coal and spent water is pumped to the surface for cleaning and clarification. About 4,000 hp of hydraulic energy is provided to each of the three monitors, one in each seam. This energy, together with an induced caving system, is expected to produce over 1,400 tons of raw coal per monitor shift. Only 3% of the coal mined comes from development, which is accomplished by roadheader-type machines. Capital costs are estimated at $88 million including interest during construction, for a produciton of 3 mmtpy. The internal rate of return ranges from 18% to 27%, based on sales prices from $21 to $26 per ton, free on rail. Overall productivity is estimated at 42 tons per employee shift, and recovery is estimated at 60%. Safety is further enhanced by reduction of dust and by remote controlled extraction of top coal and pillars. Recovery and productivity are improved over those of any other underground mining method for such thick seams.