HOUSTON, Feb. 11 — The former trading business of Enron Corp., shut down since early December, is up and running again under the name of UBS Warburg Energy.

Financial gas and power trading is taking place but no physical products are traded yet, the company said. Trading operations commenced in Houston at what was to have been a new headquarters building for Enron Corp., which stands mostly empty except for two floors occupied by UBS Warburg.

The trading floor is being operated with the same senior management team and traders that built the Enron energy trading business, UBS Warburg said in a statement. The trading operation has financial swaps and options available on line with a variety of terms and locations, said Jennifer Walker, spokeswoman. Physical products are not being traded yet, she said.

“We are in the process of securing regulatory approvals and licenses for the physical products,” she said.

The former Enrononline.com was once a “market maker,” meaning other traders looked to Enron to establish trading price ranges. But so far the new UBSWenergy.com is only trading on the New York Mercantile Exchange and not yet trading with other energy companies, industry sources said.

“Customers are in the process of getting their transaction Ids (identifications) in order,” Walker said “They can start trading when the credit and legal processes are finished.”

A Reliant Energy Inc. spokesman said UBS Warburg had contacted the company recently about starting the documentation required to restart trading. Documentation is in the process of being evaluated, said Richard Wheatley, spokesman for Reliant. Dynegy Inc. and El Paso Corp. were not sure if they had initiated steps yet to trade with UBS Warburg, spokesman for both companies said.

Traders on the floor of another large energy marketing and trading organization said their credit desk had not said when trading could begin with UBS Warburg. “We haven’t heard anything yet,” said one spread option trader.

Traders adjusted operations to accommodate the loss of Enron Online, he said. At first volume declined. But the net result of Enron Online’s shutting down was just the loss of one counterparty, he said. “Everybody just made it up with other counterparties,” he said.

UBS Warburg said all transactions done on the web site will be backed by the AA+ investment grade credit rating of UBS AG, the Swiss bank parent of UBS Warburg. The new organization did not assume any past, present, or future liabilities of Enron or its previous trading positions, it said.