Fuel consumption increases during winter?

I guess that if the answer is "yes" then the difference will be neglectable, but anyway...
I was wondering if during winter, fuel is less efficient than summer. During summer, there is some extra energy content in the fuel, due to increased temperature. This extra energy is added to the energy of the gas after the combustion and contributes in the production of work, so fuel during summer will offer more work. Is there something that I am missing here?