So I have a question concerning third party liability insurance for rental cars in Portugal. I was having a hard time finding any information on prices for supplemental third party liability insurance. I want to use my AMEX premium car insurance with additional supplemental because AMEX does not cover this. I read on this site that third party liability insurance is mandatory on all rentals. Can anyone confirm this? Also, if anyone has any insurance advice for renting Portugal I could use it, normally I just use taxis and public transport when I travel internationally.