The S&P Dow Jones Indices parent had offered to buy MSCI for $120 a share, the London newspaper said, citing people familiar with the matter. The sources also told the paper that MSCI shareholders are holding out for a buyout to the tune of $12 billion, or $130 per share.
S&P Dow Jones did not immediately respond to CNBC's request for comment.
Later on Wednesday, MSCI said in a statement that while it does not normally comment on market rumors, it said it isn't in discussions with third parties and hasn't received an offer or indication of interest.
Shares of MSCI rose more than 10 percent, hitting record highs in intraday trading. The stock later pared its gains, but still ended the session 3 percent higher. With Wednesday's gains, shares are up more than 26 percent for the year so far.
Formerly part of Morgan Stanley, MSCI compiles global benchmark indexes such as the All-Country World Index and the Emerging Markets Index.