Fuel oil
Additionally in 1956 engine 01 1100 received an oil-firing, enhancing its performance considerably. Oil-firing allows for a better control of the grate and could be more easily adapted to respective operating conditions. The engines were therefore more economical than coal-fired locomotives. Working conditions for firemen were also improved. Fuel oil, then available as a waste product, was used for firing. Following their positive experience with 01 1100, the DB decided in 1957 to convert another 33 locomotives of this class to oil-firing.