The goal of this thesis is to examine dualueling concepts using two different types of primary fuel, methane and propane; as well as two different pilot fuels, ultra-low sulfur diesel (ULSD) and biodiesel (B100). Experiments were performed using a 1.9 liter, turbocharged, 4 cylinder diesel engine at 1800 rev/min with ULSD and B100 being injected as a pilot fuel directly into the combustion chamber, at different brake mean effective pressures (BMEP), and percent energy substitutions of propane and methane. Brake thermal efficiency (BTE) and emissions (NOx, THC, CO, CO2, O2 and smoke) were also measured and analyzed. Maximum PES was limited by misfire at 2.5 bar, 5.0 bar, 7.5 bar, BMEP for all cases and knock at 10 bar BMEP for both B100-propane and ULSD-propane. In general dual fueling was shown to be beneficial for lowering NOx, CO2, and smoke emissions along with, in some cases, showing improvements in BTE.