US regulators revealed a wide-ranging investigation into crude oil trading practices on Thursday amid increasing congressional concern over the role of speculators in record energy prices.

Citing "today's unprecedented market conditions", the Commodity Futures Trading Commission said it was breaking with its customary secrecy to disclose that since December 2007 it had been investigating "the purchase, transportation, storage, and trading of crude oil and related derivative contracts".

The statement came as the agency tightened its oversight of oil and energy derivatives markets by agreeing to share more information on traders' positions in key energy contracts with the UK's Financial Services Authority.

Both measures come as congressional scrutiny of energy markets is rising. Top Democrats this month held hearings into the role of speculators in oil's recent rise to a record $135.09 a barrel.

The CFTC said its agreement with the FSA would expand information-sharing for contracts with US physical delivery points - such as the benchmark West Texas Intermediate crude oil future. The agreement also involves the InterContinental Exchange (ICE), an operator of energy derivatives markets in the US and UK.

This month, the CFTC's chief economist told a congressional hearing that it believed "broad-based manipulative forces" were "not driving the recent higher futures prices in commodities across-the-board".

It said on Thursday that the new "measures will expand the amount and quality of information received from energy traders to further the integrity and oversight of our nation's futures markets."

The FSA is involved because it oversees ICE's London-based energy derivatives market, ICE Futures Europe - formerly the International Petroleum Exchange.

The WTI contract is the US crude oil benchmark contract, but about 25 per cent of its trading volume is carried out in London on ICE. The rest is traded on the New York Mercantile Exchange. Under the new arrangement, the FSA, CFTC and ICE will share more information about traders' positions in WTI contracts in London and New York.

ICE said it had "facilitated" the agreement with the FSA and CFTC "to provide enhancements to its energy market data reporting, including the large trader reports already in place on its WTI crude oil futures contract".