I have a friend who I take out on my boat very often fishing. Grant
it, it is a small boat 16' 6". But it still runs on fuel. He never has
offered to pay for fuel or help to wash all the crude out of it from
fishing. I did invite him to go so I do not feel right asking him. For
example yesterday we went fishing at small lake. I drove my truck,
towing my boat 140+ miles round trip, used 6 gallons of fuel on the
lake. I know that is not a lot since some people here have boats that
use 6 gallons just to start. But, he could offer.
Another example last year we went to Canada for a "guys" week. We used
60-70 gallons of fuel running around a much bigger lake (Bobs Lake if
anyone knows where that is) that week. That is not including the 70-80
gallons to get there and back. He did not offer cash for gas. But, he
did pay his share of the house and food.

I hope you didn't clean his fish for him also on that trip
after you paid the gas....

I always offer to pay for gas or help pay for part of it, etc.
I also try to be the one who brings to cooler of drinks/snacks
if I'm going out on someone elses boat.

I don't always find people doing this when they go out on my
boat. If it's someone who does offer, its because they too
know what a boat operation coats, not to mention monthly
payments, insurance, fee's, registration, maintenance, etc
and they are usually a boat owner also.

I've never asked for gas money, but personally I think it's
the right thing to offer if you are going out on someone elses
boat, even if you are a guest. Especially if it's a trip
where a lot of gas is consumed. If they don't pay, not a big
deal. I knew that boats cost money when I bought it. I don't
ever get $$$ amount of money from everyone, it's just sometimes
someone will bring a cooler of something or offer to pay
when we are at the pump. It's funny to see a non boater
realize how much gas was used and what it costs compared
to prices of gas bought for a car.

-mike