Wal-Mart Stores Inc. dethroned Exxon Mobil Corp. to win back first place on the 2007 Fortune 500 list after a confluence of economic forces led American companies to their most profitable year in the compilation’s 53-year history. The big retailer posted a more than 11% increase in revenue to $351.1 billion and profits of $11.3 billion, according to the magazine’s annual ranking of the nation’s largest companies. The discounter has topped the list five out of the last six years. Fortune compiled the rankings based on companies’ 2006 revenues. Nipping at Wal-Mart’s heels was 2006 titleholder Exxon Mobil, which had $347.3 billion in revenue and the highest profit in history by an American company, reaching $39.5 billion.