[drcoastline]

Insurance companies are rated by the A.M. Best Company. There are other rating companies as well but A.M. Best is the standard bearer for rating insurers. Ratings are similar to stock ratings. A++ is the highest rating for admitted carriers (State Farm, Allstate, etc.) The ratings decline from there. A+, A, B++, B+, B, etc. Never insure with a carrier below an B.

The ratings are given by financial reserves vs. risk.

It is quite likely Earthquake insurance will be excluded by the standard policy and issued through an excess/surplus lines carrier (Lloyd's, Scottsdale, Pacific, etc.) There rating shows financial strength. It can be compared to the Standard market ratings to give you a barometer as to their stability. EDIT: The excess/surplus market doesn't receive the A++, etc. rating. So you need to compare to the standard market to get an idea of strength.