It's mandatory in Oregon and New Jersey. Which are not exactly Wyoming, in terms of population, but they are just two states. Outside of that, there's a full-s

It's mandatory in Oregon and New Jersey. Which are not exactly Wyoming, in terms of population, but they are just two states. Outside of that, there's a full-service station down the street from me, but it's about 30 cents per gallon more to get full service (though it is full service and they will check your oil, tire pressure, coolant, windshield washer fluid, etc., and refill the washer fluid and air up tires). It's the only one I know of at all outside of those two states (though of course there must be others still out there).