I am trying to rent an all-wheel-drive or 4-wheel-drive (AWD or 4WD) car. However, none of the sites I normally use to look for cars (AutoSlash, Kayak, CarRentals, directly at a few rental companies' websites, etc) say whether the car will be AWD/4WD or not. I can select "SUV" as the car type, but many SUV models can be either 2WD or 4WD/AWD. As I understand it, car rental companies typically have a mixture of both in their fleets.
I've heard of some people successfully reserving a 4WD/AWD vehicle by calling the rental company or by filling in the "special requests" field during reservation. However, these solutions are not ideal since nothing is guaranteed in writing by the can rental company. I don't want to pay a premium for reserving an SUV only to find out at the rental counter that I get a 2WD one.
So, is there a way to reliably reserve a 4WD/AWD car online from a major car rental company? Note that I'm not looking for specialized "adventure/offroading" companies, but rather the typical car rental companies you would find around an airport. San Francisco / SFO is the one I'm most interested in for the purposes of this question. This is to have an extra level of safety if I happen to take a trip higher in the mountains in snowy conditions, and to be able to handle condition R1 listed here, and not for some crazy offroading adventure.