Walmart is once again America's grocery king, but rival Costco is rapidly gaining ground

Source: Business Insider

It would take the four largest pure-play grocery chains combined — Kroger, Albertsons, Publix, and Ahold Delhaize — to finally outsize Walmart's grocery sales. Frederic J. Brown/AFP via Getty ImagesMore than one in five US grocery dollars is being spent at Walmart, for the third year in a row.