An emissions and performance study was conducted to explore the effects of exhaust gas recirculation (EGR) and multiple injections on the emission of oxides of nitrogen (NOx), particulate emissions, and brake specific fuel consumption (BSFC) over a wide range of engine operating conditions. The tests were conducted on an instrumented single cylinder version of the Caterpillar 3400 series heavy duty Diesel engine. Data was taken at 1600 rev/min, and 75% load, and also at operating conditions taken from a 6-mode simulation of the federal transient test procedure (FTP). The fuel system used was an electronically controlled, common rail injector and supporting hardware. The fuel system was capable of as many as four independent injections per combustion event at pressures from 20 to 120MPa. NOx versus particulate trade-off curves were generated over a range of injection timings for each mode in a baseline condition, then trade-off curves were generated for several of the modes using multiple injections and/or EGR. A previous study, conducted at 1600 rev/min, and 75% of peak torque showed that by using an optimal triple injection, and a 6% EGR rate, NOx and particulate could be simultaneously reduced to as low as 2.2 and 0.07 g/bhp-hr, respectively. The present results first show that at the 1600 rev/min, 75% load running condition, NOx and particulate emissions can be further reduced to 1.58 g/bhp-hr NOx with 0.105 g/bhp-hr particulate by using 10% EGR with an optimized quadruple injection. The present results also show that NOx and particulate emissions as well as fuel consumption can be reduced over the entire engine operating map with the use of multiple injections and EGR. The emissions reductions effected on the test engine, through the use of optimized injection pressures, multiple injections and EGR, allowed an overall cycle emissions reduction from 5.17 g/bhp-hr NOx with 0.44 g/bhp-hr particulate to 3.70 g/bhp-hr NOx with 0.11 g/bhp-hr particulate while providing a reduction in overall cycle BSFC from 206 g/bhp-hr to 184 g/bhp-hr. When corrected to account for the reduced frictional losses of a multi-cylinder engine, these emission levels are in compliance with 1998 US EPA mandates.