Citigroup's Houston energy trading unit, once offered up for sale, hired more than 30 people including former Enron executive Vincent Kaminski.

The operation now employs 40, including five executives who relocated from New York, Citigroup spokesman Joe Christinat said. The bank's Houston desk trades natural gas, electricity and crude oil, and plans to add coal and emissions.

Citigroup and rivals banks such as Merrill Lynch are returning to a business they once shunned as too volatile. Led by surging energy prices, Morgan Stanley and Goldman Sachs Group both generated more than US$1 billion of revenue from energy trading last year. Oil prices have topped a record US$60 a barrel on the New York Mercantile Exchange.

"If they're going at the business from the standpoint of oil and refined-product trading, they could very well be late to the party,'' said Ethan Ravage, a San Francisco energy-trading consultant for the financial services industry. "If they're focusing on power trading, there's more room there.''

Citigroup's Houston trading desk reports to Stuart Staley, a New York-based head of commodity derivatives. The company hired Kaminski, 57, as a managing director in March. Kaminski had worked at Enron for a decade and was credited with developing mathematical models to value energy transactions and assess risks. Kaminski left Enron in 2002.

He had warned Enron executives of the improprieties of the company's off-the-books partnerships as early as 1999, according to 2002 reports by the Wall Street Journal and Washington Post. Transactions related to those partnerships led to Enron's collapse and bankruptcy in December 2001.

Merrill returned to the US$60 billion-a-day energy-trading market in November after an absence of more than three years by buying Entergy-Koch's energy-trading unit for US$800 million. That group also is based in Houston.

JPMorgan Chase hired four executives in March for its energy-trading business, including Morgan Stanley's George "Beau'' Taylor. The unit has more than doubled in size since the start of 2004.

Lehman Brothers Holdings has run advertisements this month seeking job candidates with "significant industry experience'' in energy trading.

Goldman and Morgan Stanley both have more than 200 employees in their commodities trading units, which can also handle physical trading, or take actual delivery of tankers of crude.

"It's a tough time for anyone getting into this market,'' said Justin Pearson, who in January 2003 co-founded a London headhunting firm for the energy and commodities fields, three months after TXU Corp and Dynegy quit trading in Europe. "They've got a big chore ahead of them. They have to do something to differentiate themselves.''