The CME Group is set to enhance its position as the world’s biggest exchange after finalising a deal to buy Nymex for $9.4bn in cash and shares, providing a rare bright spot on a grim day for financial markets.

The deal will create a company that controls about 98 per cent of US-listed futures and offers contracts on a wide range of underlying commodities and events such as interest rates, foreign exchange, stock indices, oil, metals and agricultural products.