In the trading chain

Trading on information gleaned from a subsidiary like TransMontaigne would be illegal in the stock market, but there are no rules against it in commodities. Morgan Stanley also holds a stake Heidmar Holdings, of Norwalk, Conn., which owns a fleet of oil tankers.Saule T. Omarova, an associate professor of law at the University of North Carolina at Chapel Hill, said Morgan Stanley's overlapping activities illustrate how large financial institutions have become deeply entwined in every aspect of the commodities markets.

"In the trading chain between the oil well and the gas station," Ms. Omarova said, "Morgan Stanley is clearly accumulating as many stakes along the way as possible because that is what gives them the most flexibility of control." Officials at the E.P.A., which oversees the market, say they have seen no evidence of improper trading, like hoarding, in the market. But they do not police the RIN market as a financial regulator would. "If there were any evidence now or in the future that that was happening, we have the ability to amend the regulation to constrain that," said Christopher Grundler, director of E.P.A.'s office of transportation and air quality, which oversees the renewable fuels program.

It is difficult for outside groups, or even other regulators and law enforcement agencies, to keep tabs on the market, because the E.P.A. declines to disclose who actively trades the credits, or how much they trade, citing the confidentiality of refiners and other participants.Trading is a private affair, usually conducted by phone, and just about anyone can participate. In creating the market, the E.P.A. says it did not limit the market for RINs to refiners and other energy companies because it wanted to encourage a free market.

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