U.S. sales by the 20 largest food retailers totaled $404.2 billion in 2009, amounting to 64.2 percent of U.S. grocery store sales, an increase from 39.2 percent in 1992. Although shares held by the largest 4, 8, and 20 supermarket and supercenter retailers decreased slightly from 2008 to 2009, the longer term trend shows an increasing concentration of sales among the Nation’s largest grocery retailers. Contributing factors to these increases over the past decade include mergers and acquisitions among food retailers and the rapid growth of Wal-Mart supercenters.
source: usda