This paper presents experimental results concerning the comparative monitoring of the LPG (Liquid Petroleum Gas) and Petrol fuel combustion which supplies an electrical generator driven by an internal combustion system. The main pollutants HC, CO, CO(2), NO(X), are monitored and the consequences on the cogeneration system are shown. The results indicate that even the LPG is a less polluting gas, for a nominal charge of the engine (2 kW), the amount of exhaust greenhouse gases is increased (CO(2)); on the other hand the price for LPG (low cost in comparison to fossil gasoline/petrol) is an advantage.