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* Source says Dutch trader Argos Energies being investigated
* Sen. Wyden calls for Justice Dept to look at US priceimpact
* Finnish refiner Neste Oil says asked for information
* Oil market liquidity not affected -Platts
By Simon Falush and Timothy Gardner
LONDON/WASHINGTON, May 17 (Reuters) - A European probe intopossible oil price manipulation expanded with the investigationof a small niche trading house in the Netherlands and a key U.S.senator on Friday called for the Justice Department to join theinvestigation.
Dutch trading house Argos Energies, a mid-sized tradingcompany that deals in physical oil products and owns storagefacilities, was visited by inspectors from the EuropeanCommission on Tuesday, a source familiar with the investigationsaid on Friday.
The visit occurred on the same day that authorities raidedthe London bureau of pricing agency Platts, and the offices ofStatoil, Royal Dutch Shell and BP inthe biggest cross-border action since the probe into rigging ofLibor benchmark interest rates.
In Washington, the chairman of the Senate's energy committeeasked the Justice Department to investigate whether allegedprice manipulation has boosted fuel prices for U.S. consumers.
"Efforts to manipulate the European oil indices, if proven,may have already impacted U.S. consumers and businesses, becauseof the interrelationships among world oil markets and hedgingpractices," Senator Ron Wyden, the chairman of the Senate Energyand Natural Resources Committee, wrote in a letter to AttorneyGeneral Eric Holder.
The U.S. Commodity Futures Trading Commission and FederalTrade Commission have both declined to comment on any role orcoordination with EU authorities in the probe. U.S. politiciansincluding Wyden often call for enquiries into issues that mayaffect gasoline prices, although regulators are not obligated totake action.
A spokesman for the Justice Department would not comment onwhether the agency would undertake a probe, but said it wasreviewing Wyden's letter.
Authorities have sharpened scrutiny of financial benchmarksaround the world since slapping large fines on some of theworld's biggest banks for rigging interest rate benchmarks.
Over the past year many observers have noted the resemblancebetween the Libor self-reported benchmark and the journalistassessment-based methodology used to set most of the world's oilprices, but this week's investigation is the first indicationthat EU authorities are taking a harder look at the system.
Hungary's Pannonia Ethanol, a recent entrant to Europe'smarket, was the first company to identify itself as havingcomplained to Brussels over access to the Platts market-on-close(MOC) system - a daily half-hour "window" of trading duringwhich the agency determines prices through a series of bids,offers and trades.
The source said that inspectors were still on the premisesof Argos Energies on Friday and that it was also the last day ofthe inspection at the company.
Argos Energies declined to comment.
NO IMPACT ON LIQUIDITY
Platts said trading in the oil market has not beensignificantly affected by the investigation.
"Market participation and liquidity are unchanged," Plattseditorial director Dan Tanz said.
Meanwhile Neste Oil, a Finnish refinery, said ithad received a request from the European Commission to provideinformation, although it said it was not under inspection.
"We will naturally cooperate with this request and providethe information requested to assist the European Commission inits investigation," Matti Lehmus, executive vice president, OilProducts and Renewables said in a statement.
The investigation is focused on whether there was collusionto distort prices of crude, refined oil products and ethanoltraded during the MOC window.
Platts, a unit of McGraw-Hill, provides clientswith price benchmarks set by reporters for opaque energymarkets.
Its assessments are used to close physical and derivativedeals worth billions in a $2.5 trillion market.
Thomson Reuters, parent of Reuters news, competeswith Platts in providing news and information to the oil market.
