The Bureau of Mines conducted research to simulate in situ leaching of a chalcopyrite ore. The purpose was to obtain a direct comparison between moderate-temperature and elevated-temperature in situ leaching of copper from minus 10-inch ore and to analyze the sulfuric acid and oxygen requirements of the leaching system. Experiments employing oxygen were conducted at 35 deg and 90 deg c on 362- and 367-lb ore charges, respectively, under flooded conditions and at 400 psig. At 90 deg c, 47 pct of the copper was extracted in 913 days of leaching; at 35 deg c, 27 pct of the copper was extracted in 915 days. Diffusion into and out of the ore fragments controlled the rate of leaching. Oxygen consumption was 1.46 Lb/lb of copper extracted at 35 deg c and 3.15 Lb/lb of copper extracted at 90 deg c. Sulfuric acid requirements of the ore were 5.49 and 7.48 Lb/lb of copper extracted at 35 deg and 90 deg c, respectively.