While such contracts are often used to hedge risk or to engage in market speculation, lobbyists have raised concerns about what happens to firms that actually physically settle these forward contracts.
The Commodity Markets Council, in a recent memo, contended that subjecting such contracts to the same regulations as derivatives — instruments based on some form of underlying financial security — would require some companies to restructure their business models and potentially force them to be regulated like investment firms.
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That could sap the profitability of nonfinancial businesses like "a company in Germany that buys and sells barge-borne cargoes of petroleum products," the group wrote, or "an independent U.K. power generator that sells electricity but engages in no financial trading."
David Reed, a partner here in Brussels at the lobbying firm Kreab Gavin Anderson, whose clients include finance and energy companies, said, "Particular attention should be paid to energy products in order to avoid unintended consequences" — particularly subjecting them to trading costs that could drive up energy prices for consumers.
Such arguments have held sway with the Council of the European Union. At the meeting last month, the council proposed to exempt many types of oil and energy contracts from the new regulations, according to accounts of people who attended.
Ms. Bowles sided with the council. Regulating physically settled forward contracts, she said, "would add to energy costs but for no purpose."
But the European Commission balked at that idea last month. It argued at the December meeting that such products should not be left unregulated and should be exempted only if they were subject to a separate European regulation related to gas and electricity contracts.
"The commission believes physically settled forwards should be subject to the same regulatory standards as other similar instruments," Michel Barnier, a Frenchman who is the top commission official overseeing the issue, said in a statement on Monday. He said he was "confident and hopeful" that an agreement would be reached on Tuesday, adding that it would "represent a key step toward establishing a safer, sounder and more responsible financial system and restoring investor confidence."
At the December 18 meeting, as negotiations stretched late into the night, signs of frustration became evident.
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Tweets by Ms. Bowles became increasingly acerbic. "Everyone back in the room, but still four different conversations going on," read one. Later, referring to nongovernmental organizations, she wrote, "Compromises won't happen, fear of N.G.O.'s berating even tentative deals. So will end up with nothing."
And then, as often happens in European negotiations, fissures among the chief nations emerged. Ms. Bowles tweeted, "Strangely the only things introduced by the commission appear to be French concerns …"
In a retort to Ms. Bowles, Mr. Barnier wrote in his own tweet that he was concerned with "Transparency, access & fair competition" and that the "commission wants fair deal 4 investors & consumers."
On Tuesday, one key dynamic will be different — the council's presidency has rotated from the Lithuanians to the Greeks. And the new temporary Greek leadership has been trying to broker a complex compromise in recent days. Among other things, Greek officials are proposing to waive clearing obligations for the kinds of contracts that are in dispute, which could prevent them from incurring new trading costs.
It was unclear, however, whether the latest proposal would be acceptable to all sides.
As Sven Giegold of Germany, a Green Party member who was at the December meeting, put it, "This question is now the deal breaker."