CME, owner of the Chicago Mercantile Exchange and the Chicago Board of Trade, announced its intentions of purchasing Nymex Holdings Inc. (NYSE:NMX) in March, and has since raised its offer for the New York exchange's membership seats from $612,000 to $750,000, the Chicago Sun Times reported Saturday.

Analysts say the deal is worth more than $6 billion and also includes an offer to Nymex's shareholders of $36 per share in cash and one-tenth of a share of CME Group stock for every Nymex share held. The newspaper said CME Chief Executive Craig Donohue is working to smooth over opposition to the deal among some Nymex members, who believe they should be getting a richer offer in light of a recent tumble in CME Group's stock price.

"It's the back door to try to get a deal done," Justin Lumiere, a New York-based analyst at brokerage ICAP, told the Sun-Times. "There is a higher probability now that the vote will go through, now that they've increased the seat consideration. But this is not a slam-dunk."