Source: Adapted from Endresen, Ø., Sørgård, E., Behrens, H.L., Brett, P.O., and Isaksen, I.S.A. (2007) “A historical reconstruction of ships’ fuel consumption and emissions”, J. Geophys. Res.-Atmos., 112, D12301.
The transition from coal to bunker oil as the main fuel for maritime shipping mainly took place between 1920 and 1950. During this phase, the tonnage of commercial bunker fuel declined, particularly between 1929 and 1950. The main reason is that marine fuel oil (usually bunker C) is about 40% more energy-intensive than bituminous coal per unit of weight. With the same fuel efficiency, an oil-powered ship requires 40% less fuel mass to perform the same voyage. Another factor was the global economic depression in the 1930s, which reduced shipping demand, and World War II, which created substantial disruptions in commercial shipping. By the mid-1950s, global shipping grew rapidly, and the transition from coal to oil was completed, leaving old coal-powered ships to be retired and scrapped.