my buddy has a civic hybrid and hes actually running a 1500 watt amp powering a JL W7 sub. All i can say is he gets better gas mileage than me still and im in a 01 accord sedan which gets decent gas milage as it is. He actually refills every 4-5 days and he drives A LOT. So if it infact does decrease gas mileage, it is so minimal. I wouldnt worry about it, and if your as addicted to music as we are its worth the couple of mpg decrease. Hope this helps some