ntercontinentalExchange Inc. said Wednesday it reached a deal that in effect sweetens the Atlanta energy exchange operator's bid to buy the Chicago Board of Trade, putting more pressure on rival bidder, the Chicago Mercantile Exchange. The agreement involves the Chicago Board Options Exchange - long affiliated with CBOT - and would give Board of Trade members more cash if the ICE-CBOT deal goes through. Analysts said the move gives ICE a better chance of outmaneuvering the Chicago Mercantile Exchange (nyse: CME - news - people )'s parent company for an acquisition that once seemed all but assured to go to the Merc. ICE and the options exchange said they would pay CBOT members who own CBOE exercise rights $500,000 in cash or securities for each right. The move, which could cost up to $665.5 million, places a value on rights that are at the center of a legal dispute between CBOT and CBOE members over ownership of the options exchange. ICE and CBOE would each foot half the bill. The offer is contingent on ICE's acquiring CBOT Holdings Inc., the parent company of the Board of Trade. ICE is bidding against Chicago Mercantile Exchange Holdings Inc. to buy the country's oldest futures exchange. Last week the Chicago Merc, which operates the country's largest futures exchange, boosted its bid 16 percent, gaining approval from the CBOT board, which deemed the offer superior to ICE's. But some Board of Trade members expressed displeasure that the Merc's bid remains below the one from ICE, leaving the outcome unclear. Shareholders, a majority of them BOT members, are scheduled to vote on the deal July 9. Analyst Christopher Allen of Bank of America (nyse: BAC - news - people ) Securities said the deal increases the probability that ICE could prevail in the bidding. Rob Rutschow of Deutsche Bank (nyse: DB - news - people ) agreed, although he doesn't think it is enough to tip the scales for ICE. "We still continue to believe that if CME gets Department of Justice approval, that it will be the eventual winner in the CBOT bidding," he wrote in a note to investors. "However, ICE is making all of the right moves to try to win the bid, and we view this as a very smart maneuver on ICE's part to help shore up its support among its toughest constituency." ICE, an upstart that last year bought the New York Board of Trade, started the duel by making an unsolicited bid that was higher than Chicago Merc's initial offer. CBOE was formed by CBOT members three decades ago, but the two have been in a legal dispute over how much of CBOE is owned by CBOT. The proposed deal would end that legal battle by paying CBOT members holding the exercise rights either cash or equity in CBOE. CBOE is making the deal because it would allow the options exchange to convert into a holding company. The deal also includes an agreement between ICE and CBOE on technology and product development. Shares in CBOT Holdings rose $4, or 2.1 percent, to $196.97 in morning trading. ICE shares declined 12 cents to $147.63, while CME fell $3.92 to $522.10.