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S&P 500 soon to have 505 listed shares

21st Century Fox
Scott Mlyn | CNBC

The Standard & Poor's 500 will soon contain 505 listed stocks, up from the current 502 listed stocks.

S&P Dow Jones Indices, which oversees the benchmark index of large U.S. stocks, on Monday announced a methodology change that will cause three more companies to have multiple listings: Comcast, News Corp., and 21st Century Fox. (Disclosure: Comcast is the parent of NBCUniversal and CNBC.)

The change follows a move made in January to allow multiple share classes in S&P indexes. It will take effect after the close of trading on Sept. 18, to coincide with a quarterly rebalancing.

Google and Discovery Communications already are represented by two share class lines each in the S&P 500 index.

Warren Buffett's Berkshire Hathaway, which also has two share classes, is an exception because its Class A shares are not heavily traded, and only its Class B shares are reflected in the index.