In an article I read in Cessna Flyer last night, it reported that 100LL is 5.87 lbs/gal., but the 100UL is 6.3 lbs/gal. So for 74 gallons in my 182, it's about a 32 lb. "penalty" -- or, to put it differently, I could carry 5 less gallons if I wanted to maintain the same fuel weigh. Smaller...