The potential of biodiesel fuels from various vegetable oil sources such as sunflower (SFME), safflower (SAFME), peanut (PME) and canola (CME) as well as from low-cost chicken fat (CFME) to supplement increasing biodiesel demands must be evaluated in terms of the corresponding engine performance and exhaust emissions. In this study, two diesel engines rated at 14.2 kW (small) and 60 kW (large) were operated by using the different biodiesel fuels and a reference diesel. Results showed that both the small and large engines delivered similar power when using biodiesel fuels in the expense of higher brake-specific fuel consumptions (BSFC). Higher exhaust concentrations of nitrogen oxides (NOx) and carbon dioxide (CO2) while lower carbon dioxide (CO) and negligible sulfur dioxide (SO2) emissions were observed in both engines. Total hydrocarbon emissions (THC) were higher in both engines when using SME, SFME and CME but comparable when using CFME, SAFME and PME in the large engine. Thus, with the increasing demand for biodiesel, alternative feedstock sources such as those used in this study may be utilized to take advantage of their availability, renewability and environmental benefits.