30 biggest S&P 500 stocks Below is an updated rating of the largest S&P 500 companies. Apple (AAPL), which ranks first, has a market cap of over USD 600 bn as of the date on which this report was released. This means the company is worth nearly USD180 bn more than Exxon Mobil (XOM), the next largest company on the list. The difference in market cap between Apple and Exxon is equivalent to the size of AT&T, the 19th biggest company. Google (GOOGL), which lags quite far behind XOM, ranks third. Then comes Microsoft (MSFT), which has surged in 2014, adding USD 74 bn to its market cap, which currently totals USD 386.4 bn. Berkshire Hathaway (BRK/B) rounds out the top five with a market cap of USD 339.5 bn. No other companies are valued at more than USD 300 bn, but Johnson & Johnson (JNJ) is close at USD 296 bn.