Reciprocating internal combustion engines are a mature technology used for power generation, transportation, and many other purposes. For CHP installations, reciprocating engines have capacities that range from 10 kW to 10 MW. Reciprocating engines for distributed power generation, which are most often fueled with natural gas, are well suited for CHP service. There are nearly 2,400 reciprocating engine CHP installations in the United States, accounting for 54% of the entire population of installed CHP systems and nearly 2.4 gigawatts (GW) of total capacity. Common applications for reciprocating engine CHP systems include universities, hospitals, water treatment facilities, industrial facilities, commercial buildings, and multi-family dwellings.