After having imposed limits on the trading of oil futures, US authorities have started cracking down on entities who they feel have been manipulating prices. In the first such move, commodity regulators in Washington on Thursday accused a Dutch trading company of manipulating the prices of crude oil, heating oil and gasoline over an 11-day period last year. (See: Wall Street resists tougher oil futures legislation as regulators in the US, UK agree to impose limits)

The US Commodity Futures Trading Commission (CFTC) complaint, filed as a civil lawsuit in Federal District Court in Manhattan, relates to Optiver Holding and two subsidiaries. Bastiaan van Kempen, the boss of Chicago-based Optiver, a subsidiary of Optiver Holding, was named as a defendant along with trader Christopher Dowson and Randal Meijer, a supervisor of Optiver.

According to the complaint, the employees carried out a manipulative scheme known as "banging" or "marking" the close. "Banging the close" refers to the practice of acquiring a substantial position leading up to the closing period, followed by offsetting the position before the end of trading for the purpose of attempting to manipulate prices.

The agency said the employees in three instances forced futures prices lower and in two instances caused prices to rise. Thus, out of a total of 19 attempts, five were successful allegedly netting the suspects a rich haul of $1 million.

''These charges go to the heart of the CFTC's core mission of detecting and rooting out illegal manipulation of the markets,'' said Walter L Lukken, acting chairman of the commission. He said commodity regulators had worked with exchange officials to ''stop the scheme in its tracks,'' though the follow-up investigation into Optiver's trading took longer.

The complaint also charged two of the executives with covering up the scheme by lying to the compliance staff at the New York Mercantile Exchange, known as the NYMEX, where the trading occurred in March 2007.

Regulators sometimes have difficulty demonstrating an illegal intent behind trades. In this case, regulators said, the Optiver traders were caught by their own words - extensive e-mail messages and recorded telephone calls made during the period scrutinized by regulators.

The agency's enforcement action came a day before the Senate was scheduled to have a major vote on legislation to rein in excessive energy speculation and impose new regulations on traders that the CFTC would have to enforce.

The CFTC's acting enforcement director, Stephen Obie, denied that the announcement of the case was timed to influence the vote on the bill. "This was not a politically motivated case," he said. However, Obie said the case shows that the CFTC has broad powers to police the markets.

In a statement, Optiver Holding said: "We have learned that the US Commodity Futures Trading Commission has filed a civil lawsuit against Optiver. We have received a copy of the complaint and are reviewing it. We take the CFTC's action very seriously and are treating it with the utmost attention and care."