Oops, my bad - hadn't had my morning coffee before I typed that. Thanks for picking that up! I meant to say supplemental liability (oftentimes shown as SLI or LSI).

I'm pretty sure most states require it as basic car insurance if you register/own a car. However, if you don't own a car and use your credit card when renting thinking that you're covered if you get in an accident, there's a good chance you're not in that area.