Originally Posted by Double-Trinity

As far as mileage hits go, you'd probably see about the same amount of extra fuel consumption in absolute terms on a gas-only vehicle, and a hybrid (all things equal). However because hybrids are so efficient in general, that will represent a 6-7% hit instead of a 3-4% hit. The same is true of running Air Conditioner -- the same amount of gas burned might be a 12% hit on a hybrid, and a 1% hit on a huge SUV, having that huge MPG display in front of you though makes the whole deal seem a lot worse.