I just got a new mower with a 27hp Kohler on a 52" Hustler Z. I am figuring about 1.1 gallons an hour. I filled it up and it ran out right at 10 hours. The tanks are 12 gallons, but I only put 11 gallons in because 12 would fill it to the very top and make a mess. This mower only registers hours when the blades are running. I was able to cut 36 lawns on one tank averaging $35 per lawn. 9 of these lawns were cut with a different mower (36") in back though. I thought the 27 Kohler would cost me more in gas then my 23 Kawi (same mower only 400 more hrs) but that doesn't seem to be the case. The Kohler is a little better. One thing I noticed is that the Kohler doesn't work as hard as the 23 Kawi. The 27hp on a 52" can go through some thick grass. My time spent cutting was cut way down too. I didn't have to double cut many lawns that the 23 Kawi on the same mower would have to. My 23Kawi/52 Hustler is a 2001 (Had 50hrs at the start of last year) model with 450 hrs but has the same deck etc. The other difference that might change the fuel consumption is the 23 Kawi didn't have the Donaldson air filter. I am very glad I went with the bigger engine size. A lot of people would think it is overkill, but so far it has proved to be a wise decision. Like I said gas consumption doesn't seem to be an issue and the added power has saved time. I would like to hear what some of you other guys are using per hour? Please state your engine size, make/model of engine, mower size, and make/model of mower.