Blackstone, the world's largest private-equity firm, sees commodities as another way to diversify its lines of business, one person said. The firm has grown fee-paying assets and tapped streams of revenue that are less dependent on the market cycles that drive private-equity profits.

Mercuria would gain oil infrastructure assets in North America and a global chain of warehouses for its metals trading business. Registered in Cyprus with headquarters and major trading operations in Geneva, Mercuria is the fourth-largest independent commodities trader. The company posted a profit of $343 million in 2012 on revenue of $98 billion.

Macquarie, which has an existing trading business in oil and gas, power and coal, has been expanding that business in the past years, buying a stake in British metals-warehousing company Scale Distribution last year. It is the fourth-largest trader in natural gas in North America, according to its website. Macquarie competed with JPMorgan for assets from RBS Sempra Commodities, a venture between Royal Bank of Scotland Group Plc and Sempra Energy, in 2010.

While JPMorgan's commodities unit also drew interest from Grupo BTG Pactual, the Brazilian investment bank, the bank ended its pursuit, people said this month.

KKR, which teamed up with U.S.-based energy trader Castleton Commodities International LLC, is no longer involved in the process, according to a person familiar with the situation. A spokeswoman at KKR declined to comment on its interest, while a representative for Castleton didn?¡¥t respond to a request for comment via e-mail.

Eoin Treacy's view

The CFTC is currently being lobbied by commodity consumers such as utilities, steel and chemical companies to increase restrictions on position sizing in the futures markets. Over the last decade investment banks have been able, through a roundabout mechanism, to build up substantial positions in commodity contracts well beyond what was envisaged when regulations were initially formulated. 

With such large positions, complementary warehousing operations allowed them to control aspects of both sides of the trade which has been incredibly profitable. However, the tide of regulation has turned and many of the loopholes traders benefitted from are being closed. The result is that a number of investment banks have sold their commodity infrastructure businesses and closed sales desks.   

It is reasonable to assume that the exiting of large leveraged market makers from the commodities business has been a contributory factor in the deterioration of commodity prices over the last 18 months. It is therefore interesting that as this process matures, commodities, for the most part, have either lost downward momentum or have base formation characteristics.