Wal-Mart still sits atop the Fortune 500 list

the economy. Wal-Mart was followed by the three largest American oil companies: Exxon Mobil Corp., Chevron Corp. and ConocoPhillips. Houston has 23 companies on the list. After No. 4 ConocoPhillips, Marathon Oil Corp. comes in at No. 29; Sysco at No. 67;...