We should conserve the fuel, because the fuels are getting depleted, and the chance for the fuel in the future will be less.
Then, the future generations will suffer, with the lack of fuel.
If we didn't conserve the fuels, then, there won't be any re-accomplishment.

So, it is important to conserve it, as it takes millions of years for it's formation. 
We can conserve by using battery vehicles, and limiting the usage of the vehicles.