Since this thread came up again, I'll add another data point: Couple weeks ago we picked up a minivan for the weekend out at PIT. There the agent wanted to charge us $9/day to have my girlfriend on. She said it would have been automatic if married. I'm just ordinary Gold, but I also rented on AAA CDP, which apparently covers spouse for free regardless of Gold, etc. So now I'm thinking maybe the folks at SFO just assumed we were married (well, unless the TPC CDP has some extra magic to it, which seems unlikely). Unfortuntately, just letting them assume that won't really help if something happens; what will matter at that point is how we really are related.