I have a smaller boat(sportster) with a 215hp engine. We go out and spensd about 4 hours skiing and riding around. It usually runs about 40 to 55 dollars in fuel. I would say 6 miles to the gallon maybe. The above comment is good advice. I always fill up at the gas station because marinas charge way to much. When you fill again you will see your consumption for an average day. I put a cold air intake on my boat and it seems to do a little better than with the stock air system.