With the aim to evaluate the biodiesel performance and emissions of a feedstock with promising economic and sustainability perspectives, such as waste animal fat, two biodiesel fuels, one obtained from 100% animal fat and the other from 50% soybean oil/50% animal fat, were tested in a DI common-rail diesel engine. Blends [30 and 70% (v/v)] of these two biodiesel fuels with reference diesel fuel were also tested. The pressure drop across the fuel filter was measured, and for the pure animal fat biodiesel fuel, a large increase in pressure over 5 h was recorded, indicating a clogged filter. This poor filterability should be considered by biodiesel fuel manufacturers to decide about combinations of different feedstock or additivation. Brake thermal efficiency was not affected by the use of biodiesel fuels, for both pure and blended cases. A slight increase in fuel consumption was measured for all biodiesel fuels, and it was proportional to the heating value of the fuels. Biodiesel fuels reduced hydrocarbon e...