What type of fuel should I use in the Craftsman 917.275702 lawn tractor?

Use fresh, clean, regular unleaded gasoline with a minimum of 87 octane. Do not mix oil with gasoline, and do not use leaded gasoline as it will increase carbon and lead oxide deposits and reduce valve life. Purchase fuel in quantities that can be used within 30 days to assure fuel freshness. The fuel tank holds 4 gallons. (Page 13)