Gasoline contains many hydrocarbons, but for example if you take Octane and burn it completely, you get:

2(C8H18) + 25(O2) > 16(CO2) + 18 (H20)

So for every molecule of octane you burn, you produce 8 molecules of CO2. This is ideal, not counting Nitrogen in the air and all the range of carbon chains in gasoline, but you get the idea.