Residual steam originates from two main groups in the Larderello area; the first from older wells in the urban area, and the second from more recent low production wells. The first group has very low shut-in pressure of 1 .3 to 1. 5 atmosphere (absolute) with temperatures from 105 to 110°C and 1 percent gas content. The total flow of these wells is about 25 to 30 tons (metric) per hour. The second group of wells has shut-in pressures of from 5 to 10 atmosphere, and temperatures of 140 to 190°C with 3-4 percent gas content. These wells produce about 40 tons per hour