most cities should run natural gas, capture it at their waste water plants.
natural gas has about 120 octane, so running it in a engine designed for gasoline. you will not see great mileage.. but... if the engine was built for high octane fuel.. it would get the same or better fuel economy as a engine designed and running on gasoline.
of course you would not be able to use the engine as a multi-fuel (gasoline/natural gas) vehicle with 14-16:1 compression...
thank you for the fuel tax info for Missouri.. $8.00 for 15 days of travel is a lot less than the gas taxes.. .. especially if i was to see the sights for 15 days...
you wouldn't believe how many miles traveled/gallons you can burn in 15 days...