The importance of the recycling of vegetable oils that have been used for frying has led the scientific community to provide viable options; among them is the transesterification in biodiesel. Biodiesel is one of the most popular and accepted diesel-fuel alternatives. In this sense, to gain knowledge about the implications of its use, waste olive oil methyl ester was evaluated as a fuel for diesel engines during a 50-h short-term performance test in a diesel direct-injection Perkins engine. Engine-performance tests indicated a slight power loss and brake-specific fuel consumption increase, although statistical analysis showed no significant differences between biodiesel and No. 2 diesel fuel (EN 590) tests. In this sense, energy conversion efficiency remained constant or showed a slight increase when waste olive oil methyl ester was used instead of No. 2 diesel fuel. Carbon deposits and wear seemed normal. During the test, no difficulties were experienced, in regard to engine starting, and the engine performed satisfactorily on the biodiesel throughout the entire test. On the basis of this study, waste olive oil methyl ester can be considered as a fuel candidate, thus providing an interesting alternative for the recycling of used frying oil, which is essentially a waste product. Biodiesel from used olive oil can be recommended as a diesel-fuel alternative if long-term diesel-engine tests provide satisfactory results.