I wish. There are some stations that still offer free air in the U.S. Unfortunately, they are VERY FEW. And, the few who do offer free air have intentional and unintentional restrictions on it. For examples, Intentional restriction: They turn on the compressor only if you buy something and then ASK them to. It's on a timer so that it turns off after several minutes (and thus nobody else can use it unless they buy something) It doesn't matter if you spent thousands of dollars at that gas station in the past year . . . if you aren't buying something RIGHT THEN, and need air in your tire, you are out of luck. Unintentional restrictions: The compressor at the one station in town that offers free air is BROKEN for months on end. (this one could also be INTENTIONAL, I guess)
Some gas stations have installed coin-operated air compressors. Typical cost seems to be: 50 cents (half of a U.S. Dollar, two "quarters") And of course, for your 2 quarters, the compressor only runs long enough to add a little air to one or two tires.
Of course, why would the owner of a gas station want customers to have properly inflated tires? Under-inflated tires are good for business!!!
As someone else wrote, if you live in the U.S., it's best now to own a small portable air compressor. Forget about trying to find a gas station with free air. -Dave