Both times I've used an AWD for a one-way, they charged mileage in addition to the standard fees, so the result was a ridiculously large bill. The rep I spoke with about it said that almost all the AWD codes charge mileage for one-way trips, but sometimes you can find one-ways without mileage charges on a standard rate. I haven't been real successful in that, however - I ended up renting from National instead last time. Just keep an eye out for the "Included Miles: 0" line item on the reservation.