The present study compares diesel engine performance, emissions, energy and exergy parameters of three nonedible biodiesels blends and a reference diesel. The three biodiesel blends were prepared so as to keep the blend oxygen percentage at around 3.3 wt%. Considering the economy and availability, waste cooking and macadamia (Macadamia integrifolia) biodiesels were chosen for all the engine experiments. A commercial diesel was used as a reference fuel to compare the performance and emissions with those of the biodiesel blends. To keep the oxygen percentage of the blends approximately the same as for the reference diesel, around 30% waste cooking biodiesel was added to 70% reference diesel to make the first blend. Similarly, around 30% macadamia biodiesel was mixed with 70% reference diesel to make the second blend. In addition, 10% macadamia biodiesel and 20% waste cooking biodiesel were mixed with the 70% reference diesel to make the third blend with similar oxygen content. The macadamia blend is designated as MaD, the waste cooking blend is termed WcD, and the blend with macadamia and waste cooking biodiesel is abbreviated as MaWcD. This study aimed to investigate the influence of the fuel-oxygen on engine performance, emissions, energy and exergy parameters. A well-instrumented, 4-cylinder, 4-stroke, naturally aspirated direct injection (DI) diesel engine was used for the experiments. The engine was loaded and coupled with an eddy current dynamometer. Performance, emissions, energy and exergy parameters for the three biodiesel blends were compared with those of the reference diesel. Without significant reduction in engine performance, a significant reduction in total unburnt hydrocarbon (THC), carbon monoxide (CO), and particulate matter (PM) emissions with a penalty of increased nitrogen oxides (NOx) emissions were realised with all three biodiesel blends.