) --

Royal Bank of Scotland

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and San Diego's

Sempra Energy

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are exploring the sale of their joint commodities-trading business and have engaged investment bank


to handle the sale, a report says.

RBS Sempra is seeking more than $3 billion for the entire business, the

Wall Street Journal

reports, citing people familiar with the matter. The price tag could fluctuate depending on how its trading positions are valued and how much financing RBS puts into the venture, said one person familiar with the auction process.

"This JV is a very successful business, so we expect that there will be a number of parties who will want to speak with us on this matter," said RBS spokesman Steven Blaney.

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More than 20 banks and nonfinancial companies have expressed an interest in a possible bid, sources told the


. Among those interested are

JPMorgan Chase

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Morgan Stanley

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Societe Generale

and several large oil companies.

The partners have the right of first refusal to purchase each other's stake. "We've said publicly that if we were to buy back the whole business there might be pieces we'd then sell off. Potentially we could divest certain product lines, but we've not said that we'd sell the whole business," Sempra spokesman Doug Kline told the newspaper.

European Union officials last month said RBS had to sell its 51% stake in the unit as a condition to receive state aid. The U.K. government owns 70% of RBS after a bailout last year.