Per the Avis T&Cs, coworkers (same company) are eligible to drive the car for free without any additional fees/etc. Domestic Partners, as Avis clarified recently, are those with the same license address as the renter, are also included free of charge. This Costco perk is for 1 person not falling into the above 2 categories. I've used it at a few large airports and the 2nd driver I put on the rental was always free.