A study released last week by DSR Marketing System claimed that U.S. supermarkets gained market share against warehouse clubs (i.e. Costco, BJ's) and superstores (i.e. Walmart, Target) in 2012.
The study showed that supermarkets owned a 59.3% share of grocery sales, up 0.4% from 2011. At the same time, the share of grocery sales for warehouse clubs and supercenters decreased 0.4% to 22.6%.
According to DSR, the share increase for supermarkets reflects the impact of fast-growing food retail concepts like Aldi, Kroger, Publix, Wegmans and Whole Foods, as well as closures at Kmart and slower relative growth of warehouse clubs. The company also noted that the aging population helps smaller format stores like supermarkets, since older shoppers generally dislike larger stores. (And older shoppers don't need a three-year supply of ketchup and Cheese-Its, like my family apparently does.)