Great article on this subject at:
http://www.huffingtonpost.com/george-hobica/everything-you-need-to-kn_b_3577103.html And I wonder if the coverage described in this paragraph (from article linked above) is available for rentals overseas:
What is this "primary coverage with a third party?"
Simply: It is a separate policy that protects you when you rent cars. Maybe you are protected with your credit card and your auto insurance policy, but if you get into an accident and have primary coverage elsewhere, you can leave your insurer out of the loop entirely, avoiding any potential rate increases. American Express cardholders can purchase a Premium Rental Car Protection policy for less than the cost of one day's damage waiver in many destinations. For $24.95 per rental period of up to 42 days -- $17.95 if you live in California - you've got $100,000 in coverage for damage and theft, plus $100,000 of Accidental Death or Dismemberment coverage, $15,000 for excess medical expenses and up to $5,000 for personal property loss. The real deal here? No deductible. Nada. It's a good policy. Best of all, it kicks in automatically when you begin your rental using that card. When you do, you'll be surprised at how easy it is to stop agents in their tracks - most know about the policy. Tell them you've got it and they'll generally understand that they're dealing with someone who has come prepared.