mialage is not a concern of mine go gattta buy fuel there is no way around it but i always use 93 octane do i need to or is 87 or 89 enough. the two stroke outboars on my big boat average about 2.5 when cruzen at 30 knots. but when i am at WOT and doin about 50 knots there drinking about 55 gallons per hour.