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This paper presents experimental results obtained from bench tests on a 1.4 litre, 4-cylinder, dual-fuel spark ignition engine, fitted with a three-way catalytic converter. Performance, fuel consumption and exhaust emissions measurements were recorded under steady state operating conditions from engine builds: (i) with multi-point gasoline liquid fuel injection, and (ii) with single-point vaporised LPG (propane). An after-market LPG conversion kit, incorporating electronic air-fuel ratio control based on exhaust oxygen concentration, was used in the latter case. Emissions were measured before and after the catalytic converter and catalyst conversion efficiency trends are presented for each fuel. The experimental data is also compared with predictions from a thermodynamic cycle simulation and emissions prediction model which was developed with a view to gaining an improved understanding of the observed experimental trends.