The CME Group, the world’s biggest futures exchange, said on Monday night that it was extending exclusive talks to buy Nymex, the New York exchange.

The CME – born last year from the Chicago Mercantile Exchange’s $11bn takeover of the Chicago Board of Trade – announced last month that it was in negotiations to buy the Nymex in a deal that would create the world’s largest exchange, controlling about 98 per cent of US listed futures.