The notes will pay interest semi-annually and will mature on March 15, 2013, the company said in first announcing the offer on March 3.
CME also expects to give initial purchasers an option to purchase up to $50 million of additional notes to cover over-allotments. The notes will be offered to qualified institutional buyers and can be converted into either shares of the company's Class A common stock or cash.
The notes will be senior obligations of CME and will rank equally in right of payment with its existing and future senior debt.
On Feb. 29 the Bermuda-based company released financial results for 2007 which it described as the strongest in company history.