BP faces new embarrassment in America with a court case brought by one of its former traders, who claims the company was trying to manipulate the natural gas liquids market. Drew Sickinger, who joined BP's Houston office in 2009, says the company "created a pretext" for disciplining him late last year and then unfairly dismissing him.

Filed this week in a Texan court, a lawsuit for breach of contract includes allegations that BP was trying to rig the markets "by establishing a dominant and controlling position". The court papers do not explain the basis for the rigging claims, which were immediately denied by BP. But the case is highly unwelcome for an oil company fined $300m in 2007 after trading irregularities in the propane gas market and which is still facing legal action over the Deepwater Horizon rig blowout of 2010.

BP said it never publicly discussed personnel issues or employment issues but denied it had been engaged in any illegal trading.

"Previous court settlements are a matter of record, but any additional public allegations of market misbehaviour arising from this specific legal proceeding are untrue and without merit," said a spokesman at its London headquarters. "BP is not engaging, and will not engage, in any price or market manipulation. Our ongoing trading strategies are lawful and compliant," he added.