How long will 5 gallons of gas last on 90 hp mercury?

The duration that 5 gallons of gas will last on a 90 hp Mercury outboard motor depends on several factors, including the boat's weight, speed, and operating conditions. Generally, a 90 hp outboard consumes about 10-12 gallons per hour at full throttle. Therefore, if running at full throttle, 5 gallons would last approximately 25 to 30 minutes. At lower speeds, fuel efficiency improves, potentially extending runtime significantly.