Commodity-market regulators are investigating whether energy-market players are injecting false data into the marketplace to influence perceptions about crude-oil supply and demand, people familiar with the probe say.

Among other things, regulators are concerned that companies may be reporting inventory levels that benefit their own trading positions but that may not be accurate, people familiar with the regulators' thinking say.

Unexpected drops in oil inventories reported each Wednesday by the U.S. Energy Information Administration can spark price spikes on the main oil-futures benchmark on the New York Mercantile Exchange. A company could theoretically underreport barrels in its tanks, for example, at a key hub to suggest oil is scarcer than it really is, and then sell its physical oil at a premium when oil prices jump on misleading news.

Another concern is whether companies conduct some physical oil sales and purchases solely to influence short-term pricing on oil futures markets.

It isn't clear whether the regulators, at the Commodity Futures Trading Commission, have certain energy firms in their sights. But people familiar with the agency's operations say its concerns stem from tips from sources in the oil-trading world about big market moves that occurred unexpectedly.

The commission is taking depositions, or testimony, about some of those periods, lawyers say.

The agency has become more active in soliciting and acting on leads from traders and experts in physical energy handling, according to people familiar with the commission's operations.

Among the periods the agency is examining, these people say, is a rapid shift in the structure of oil markets in July 2007. Price relationships flipped in a way that was extremely profitable for traders who may have had close knowledge of continuing and rapid drain-off in oil inventories. Oil for near-term delivery had been selling at a discount to oil to be delivered months and years into the future. Suddenly, oil for immediate delivery became much more expensive when a glut of oil at a key hub at Cushing, Okla., rapidly drained.

An agency spokeswoman said, "The CFTC has already announced one enforcement action (in July 2008) in the crude-oil markets that resulted from the agency's nationwide crude-oil investigation, and these investigative efforts are ongoing. Ensuring the integrity of the futures markets is critical, particularly in the energy sector, given the impact energy prices have on all consumers."