Here's where Americans are buying their groceries

A battle is heating up between America's top grocers, and so far, there are only a couple clear winners.

Walmart and its warehouse chain, Sam's Club, are the most dominant supermarkets in the country, accounting for more than a fifth of the grocery market share, according to data compiled by UBS.

The rest of the market is highly fragmented and split between dozens of other players, including Kroger (10%), Albertsons (5.2%) and Costco (4.2%).

Shares of grocery companies were rattled last week after it emerged that Amazon plans to acquire Whole Foods in a $13.7 billion deal. So it may come as a shock to some that Whole Foods controls just 1.4% of the market, making it the 13th largest grocery chain in America. Amazon, meanwhile, claims just 0.2% of the grocery market.

The discount store Aldi recently claimed that it will be the third largest grocery chain in the US within the next four years, thanks to an aggressive expansion plan. But for now, it claims just 1.1% of the market.

Here's the top grocery chains in America, according to UBS:

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