This research work focuses on evaluating the effect of battery state of charge (SOC) in the fuel consumption and gaseous pollutant emissions of a Toyota Prius Full Hybrid Electric Vehicle, using the Vehicle Specific Power Methodology. Information on SOC, speed and engine management was obtained from the OBD interface, with additional data collected from a 5 gas analyzer and GPS receiver with barometric altimeter. Compared with average results, 40–50% battery SOC presented higher fuel consumption (57%), as well as higher CO2 (56%), CO (27%) and NO x (55.6%) emissions. For battery SOC between 50 and 60%, fuel consumption and CO2 were 9.7% higher, CO was 1.6% lower and NO x was 20.7% lower than average. For battery SOC between 60 and 70%, fuel consumption was 3.4% lower, CO2 was 3.6% lower, CO was 6.9% higher and NO x was 24.4% higher than average. For battery SOC between 70 and 80%, fuel consumption was 39.9% lower, CO2 was 38% lower, CO was 33.9% lower and NO x was 61.4% lower than average. The effect of engine OFF periods was analyzed for CO and NO x emissions. For OFF periods higher than 30 s, increases of 63% and 73% respectively were observed.