MasterCard joins S&P 500, replaces GM in S&P 100

NEW YORK, July 10 (Reuters) - MasterCard Inc (MA.N), the world's second-largest credit card network, will replace Ace Ltd (ACE.N) in the Standard & Poor's 500 .SPX, and will also replace General Motors Corp GM.N in the S&P 100 index .OEX of major blue-chip companies, S&P said on Thursday.

S&P said it is dropping Ace from its flagship index because the insurer is reincorporating in Switzerland, rendering it ineligible for including in S&P U.S. indexes.

MasterCard shares have risen more than sixfold since the Purchase, New York-based company went public in May 2006. GM shares, meanwhile, have this year fallen to levels not seen since the 1950s.

S&P did not in a statement explain why it dropped GM from the S&P 100.

Shares of companies joining the S&P 500 often rise because many portfolio managers try to track the index, and are required to buy shares of companies that enter it.

MasterCard shares rose $9.80, or 3.9 percent, to $263 in after-hours trading following the S&P announcement. Ace shares fell $3.31, or 6.3 percent, to $49.55 after hours.

S&P said the index changes are effective after the close of trading on July 17. (Reporting by Jonathan Stempel; Editing by Carol Bishopric)