A straight-nine engine or inline-nine engine is a straight engine with nine cylinders. Straight-nine engines are usually diesel engines used for ship propulsion. Rolls-Royce Marine Engines (formerly Bergen Diesel), Pielstick and Wärtsilä (formerly Wichmann) have made this type of engine.
Straight-nine engines in current production include models in the Rolls-Royce Bergen B, C and K series, and the Wärtsilä RT-flex60C-B, RT-flex82C, RTA84T-D, RTA84C, RTA96C, 20, 26, 32, Wasa32LN, 38, 46 and 46F series. The nine cylinder versions of these engines develop power outputs from 1,620 kilowatts (2,200 PS; 2,170 hp) to 51,480 kW (69,990 PS; 69,040 hp).