Facebook is now bigger than Wal-Mart, at least when it comes to its value on the stock market.

The world's biggest online social network knocked the world's largest retailer out of the top 10 list of the highest-valued companies in the Standard & Poor's 500 index on Monday and the gap widened on Tuesday.

Facebook Inc. was valued at $242.7 billion as of late morning trading, its share price up more than 2 percent at $86.59. Wal-Mart Stores Inc., meanwhile, was valued at $233.8 billion, its stock price down 21 cents at $72.58.

Facebook has been on a roll this past year, its shares up about 32 percent in the past year compared with just 8.2 percent for the S&P 500 index. Its quarterly results have consistently surpassed expectations.