Equity Office Properties Trust made history in October 2001 as the first REIT to join the S&P 500 Index. Its sale to The Blackstone Group and subsequent exit from the index caused reverberations around the industry. However, Standard & Poor's Vice President of Index Services Alka Banerjee says growth of the REIT market both here and overseas has positioned new names to take the place of Equity Office and other REITs that have exited the indexes as the result of mergers. "Even after seven years, there doesn't seem to be an end in sight for the outperforming REIT market," Banerjee says.

Host Hotels & Resorts (NYSE: HST) and Developers Diversified Realty Corporation (NYSE: DDR) were added to the S&P 500 Index on March 19.

Earlier, on Feb. 26, American Campus Communities, Inc. (NYSE: ACC) was added to the S&P REIT Composite Index, replacing the outgoing REIT Trustreet Properties (NYSE: TSY).

Also, on April 16, Cousin Properties (NYSE: CUZ) will replace Longview Fibre in the S&P MidCap 400 Index. Tanger Factory Outlet Centers (NYSE: SKT) was added the same day to the S&P 600 Small Cap Index.

"There has been continual activity in the index with companies entering or exiting and that will continue," Banerjee says."Everyone finds REITs to be the attractive commodity right now."

There are currently 13 REITs in the S&P 500, 11 REITs in the S&P 400 Mid Cap Index and 17 REITs in the S&P 600 Small Cap Index.