The most economical steam consumptions in simple, compound, and triple engines per indicated horse-power hour have been found on trials. A simple Corliss engine has used 17 1/2 lb., and a simple Schmidt engine, with superheated steam, 17 1/5 lb. Of compound engines, several American, French, and German engines have used more than 121b. and less than 14 1b., while a triple-expansion Willans engine may use 12 3/4 lb., and a similar Sulzer engine less than 121b.