2000 model Yamaha F25 on a War Eagle. Have yet to use up a full 3 gal tank of fuel. Never looked at MPG any, but I've run the crap out of it up and down the river several times in a long day's fishing and still had a gallon and a half or so left. Tickled at the lack of fuel usage. Normally I have to throw some fuel out, aka dump it into the car or lawn mower because it goes old before I use it up.
Have also run it a lot on a larger lake trying to find Crappie, on a 3 gal tank, have run upwards of 25-28 miles and still had some left over.
Last boat was a glass bass boat with a 90hp Mariner 2 smoke. Had a 9 gallon built-in tank. Was not uncommon to use 8 gallons on basically the same lake's track, when it ran that is.