It depends on the size and volume of the tank(s) installed in the luggage compartment. CNG can only be stored in cylindrical tanks, and not toroidal tanks in the spare wheel compartment (as with LPG). For certain models of car, Bigas has developed a way of fitting CNG tanks that does not take up any space in the luggage compartment (click here for more info). You can do about 240 km on an average tank of eighty litres of CNG, which is about as far as you can go on 24 litres of petrol (gasoline). By converting the car to CNG, you can drive twice the distance because you can count on two fuel systems without having to fit tank(s) that entail reducing the size of the petrol tank.

With the same number of litres, you can drive 10-15% further on average with a petrol (gasoline) engine than you can in an LPG-fuelled car, and the distance may vary according to the tank installed. For instance, a tank fitted in the spare wheel compartment (which leaves more room in the luggage compartment) with an average volume of 38 litres of LPG, corresponding to 31 litres of petrol, lets you drive about 310 km. On the other hand, a cylindrical tank in the luggage compartment, with an average volume of 53 litres of LPG, corresponding to 43 litres of petrol, lets you drive about 430 km. Bear in mind that the distance you can drive on the petrol tank remains unchanged. Therefore the total distance you can drive is longer when you have a dual fuel system.

CNG is measured in kilograms. In general, you can do the same mileage with 1 kg of CNG as you can with 1.7 litres of petrol.

LPG is bought in litres. In general, you can do about 90% of the same mileage with a litre of LPG as you can in the same car fuelled with a litre of petrol. So if a car does 10 km with a litre of petrol, it will do 9 km with a litre of LPG. This ratio may vary depending on the propane–butane mix used.