FILE PHOTO: A BP logo is seen at a petrol station in London, Britain, January 15, 2015. REUTERS/Luke MacGregor/File Photo

LONDON (Reuters) - An unprecedented gasoline buying spree by BP BP.L in June lifted trading volumes on Europe's benchmark Argus index to the highest on record, the price reporting agency said on Friday.

Trading volumes of Argus Eurobob oxy gasoline barges totaled 449,000 tonnes in June, beating the previous record in March 2016 of 446,000 tonnes, Argus said.

BP bought 313,000 tonnes of the volume in June, the oil company’s largest purchase in a single month.

It was unclear why London-based BP, one of the world’s biggest oil traders, bought such a large volume.

Some traders attributed the move to delayed completion of maintenance at its 90,000 barrels per day Lingen refinery in northwest Germany.

A number of refineries in Germany and Switzerland went down for maintenance in recent weeks, leading to the tightening of inland fuel supplies.

Low water levels along the Rhine and Danube rivers also limited barge traffic from the Antwerp-Rotterdam-Amsterdam refining and storage hub, furthers exacerbated inland shortages.

Argus makes the bulk of its revenue by assessing energy prices and selling subscriptions to the industry.

Thomson Reuters competes with Argus in providing news and information to the oil market.