Many institutional investors, like life-insurance companies, need to match their future liabilities with the safest investments available. There’s always been an almost infinite supply of the highest-quality credits because of the enormous U.S. Treasury bond market as well as international bond markets. But as countries struggle with budgetary problems, there will be fewer and fewer top credits around. The amounts of money are so large, and the pool of corporations that have the highest financial strength is so limited, that even the shift of a small percentage of global assets could drive the prices of the most elite stocks. Some of the best will be a small group of AAA-rated international corporations. Thirty years ago, dozens of companies qualified for top credit ratings. Today only four nonfinancial stocks receive top marks from Standard & Poor’s: Automatic Data Processing, Exxon Mobil, Johnson & Johnson and Microsoft.