Fortune Magazine on Wednesday released its annual list of America's top 500 companies. This year, the combined total revenue of all 500 firms reached $12.1 trillion, representing 65% of the U.S. GDP.

Leading the way, and holding the top spot for the fifth straight year is Walmart (WMT) , with 2016 revenues totaling $485.9 billion.

Following the world's largest retailer, with last year's revenue at $223.6 billion, is Warren Buffett's Berkshire Hathaway (BRK.A) (BRK.B) .

Apple (AAPL) finished third in this year's rankings with 2016 revenues totaling $215.6 billion.

Apple is followed by the oil giant Exxon Mobil (XOM) which boasted $205 billion in revenue last year.

The fifth largest firm is McKesson (MCK) posting $192.5 billion in revenue in 2016.

Rounding out the top ten are UnitedHealth (UNH) , CVS Health (CVS) , General Motors (GM) , AT&T (T) , and Ford (F) .

Stocks have rebounded following a sharp sell off last week. Jim Cramer believes the rebound is real and gives investors advice on how to play the market going forward.

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