ah Ha, so it is true....so if my civic has a 12 Gal tank I could still add a full gallon of it, to a near full tank without any probs...I do see however that the rubbing alcohol is not the best method of raising the octane rating and the 10% mixture only raises it slightly, although it is a lot cheaper than the race gas at the track...Hmmm I usually never fill my tank all the way up, I wonder if I'm sittin between an 1/8 and a 1/4 of a tank with premuim, could I still just add one bottle of the rubbing alcohol to it and be ok. I think I would be. I'm now considering trying it the next time I go to the track...