LONDON  - Seven North Sea crude cargoes were bought and sold in the trading window operated by Platts on Thursday, a record amount that trade sources say may reflect tighter supply after Saudi Arabia's surprise output cut.

An oil trading source and an official at Platts, the price assessment agency, said that seven cargoes was believed to be a daily record in recent history. Normally, just one or two of the 600,000-barrel cargoes change hands each day.

Trade sources said the cargoes traded on Thursday comprise three cargoes of Ekofisk crude, two of Forties and one each of Oseberg and Troll. Four of the cargoes were bought by China's Unipec, the sources added.

The surge in trading of North Sea crude could reflect Saudi Arabia's announcement of a large, voluntary oil-output cut at a meeting of OPEC and its allies this week. 

"The Saudi cuts could have increased demand for barrels from outside the Gulf," a trade source said.

Saudi Arabia pledged additional cuts of one million barrels per day (bpd) in February and March as part of a deal under which most OPEC+ producers will hold production steady.

Oil supply from "the Middle East has certainly tightened up, so the Saudi cut likely has a broader impact," another trade source said of the scramble for North Sea crude.

The North Sea is the home to the dated Brent benchmark used to price oil deals around the world. Dated Brent is assessed by pricing agencies such as Platts and is based partly on trades of Brent, Ekofisk, Oseberg, Forties and Troll crude.

Reuters competes with Platts in the provision of news and pricing information about the oil market.

(Editing by Jan Harvey and Marguerita Choy) ((alex.lawler@thomsonreuters.com; +44 207 542 4087; Reuters Messaging: alex.lawler.reuters.com@reuters.net))