Swiss-based trader Gunvor, co-owned by a Russian tycoon, has bought a second European oil plant from Petroplus, as trading houses emerge as the biggest winners from the insolvent refiner's asset sale.

Petroplus' five plants came on the market at a time when trading houses, traditionally the middle-men in global oil markets, are seeking to snap up physical assets to become more like integrated oil firms as profit margins shrink.

Gunvor's purchase of the 100,000 barrel per day Ingolstadt plant in Germany, announced on Thursday, follows an agreement to buy the Antwerp refinery in Belgium in March.

"...We are delighted to have signed a purchase agreement for what will be again a key asset for Gunvor as we look to confirm our presence in Europe and diversify our trading activity in Germany," said Gunvor Chief Executive Torbjorn Tornqvist.

Gunvor said it expected to complete the purchase in the third quarter and will restart the plant as soon as possible after a three-month outage.

The expansion of traders and private investors into the European downstream market comes as majors like Total and Royal Dutch Shell seek to exit the sector suffering from thin crude oil processing margins, often by selling plants at knock-down prices.

Earlier this month rival trading house Vitol teamed up with the co-founder of Petroplus, Marcel Van Poecke, to buy the insolvent refiner's Swiss plant.

The German plant's sale will likely come as a relief to authorities after the administrator for the Petroplus Coryton plant in Britain, widely seen as the firm's most attractive asset, failed to find a buyer, endangering hundreds of jobs.

Petroplus filed for insolvency in January after it defaulted on $1.75 billion of debt.