In 43 metropolitan areas and 160 smaller markets, Walmart captures 50 percent or more of grocery sales, an in-depth analysis of 2018 spending data found. In 38 of these regions, Walmart’s share of the grocery market is 70 percent or more.

These findings provide a stark illustration of the failings of contemporary antitrust policy. They also show that more will be required to fix broken markets than reforms to merger policy.