BP shares slid yesterday after it emerged that US regulators have broadened the scope of their inquiry into alleged manipulation of the crude oil price by another three years.

In filings to the Securities and Exchange Commission, BP admitted that the US Commodity Futures Trading Commission (CFTC) and the Department of Justice had demanded documents from the company going back as far as 1999. Initially, regulators had been examining the behaviour of the oil group dating back to 2002.

The US regulators are seeking to ascertain whether the oil company sought to control the over-the-counter crude oil price and is investigating BP’s trading behaviour and its storage activities during the period.

In 2003, the company was fined after an inquiry by Nymex into claims that BP was manipulating the US exchange’s Light Sweet Crude futures contract. BP settled with a $2.5 million fine without admitting liability. After the takeover of Amoco, the US oil giant, BP acquired oil storage in Cushing, Oklahoma, which is the delivery point for the Nymex Light Sweet Crude futures contract.

In November 2006, the CFTC told BP that it would take enforcement action against the company over the way it traded gasoline futures contracts in 2002.

The gasoline case relates to BP’s position in New York Harbour, the delivery point for the Nymex gasoline contract. Because BP has no refinery in the area, it is a big local trader with terminals in Brooklyn and New Jersey. Rivals have accused BP of attempting to squeeze the gasoline market in 2002, by refusing to supply counterparts who were short of gasoline. BP had insisted that it had to supply its existing customers in a tight market.

Another wave of litigation was being prepared last summer when regulators accused BP of cornering the propane market.

The extension to the crude oil investigation comes after a miserable two years for the company. In March 2005, operational and safety deficiencies led to a fatal explosion and fire at BP’s Texas City refinery, killing 15 workers and injuring 170. Litigation from victims and families of victims is continuing.

Last year, BP partially shut down its Prudhoe Bay pipeline in Alaska, which feeds America with about a quarter of its oil supply, after leaks led to a 200,000-gallon oil spill that also sparked a criminal investigation.

In June, BP was evicted from Kovytka, a giant Siberian gas field, after the Kremlin forced the oil group into a sale of its assets to Gazprom, the Russian state-owned energy giant. At the same time, Lord Browne of Madingley, the chief executive, was forced to retire early after lying to a High Court judge about his private life.

Times Recommends

• C&G axed - 1,660 jobs to be lost
• UK house prices rise 1.1% as buyers return
• Mixed reaction to US banks repaying bailouts