By Alex Lawler
LONDON (Reuters) - Oil pricing agency S&P Global Platts (SPGI.N) is making the first major overhaul of its Brent oil price assessment in a decade, to address falling supplies of the crude oil grades underpinning the benchmark that prices most of the world's oil.
A decline in supply from North Sea fields has led to concerns that physical volumes could become too thin and hence at times could be accumulated in the hands of just a few players, making the benchmark vulnerable to manipulation.
Platts said on Monday it would add Norway's Troll to the basket of four British and Norwegian crude grades which it already uses to assess dated Brent from Jan 1. 2018. This will join Brent, Forties, Oseberg and Ekofisk, or BFOE as they are known.
"Overall we have had significant support for the addition of a new grade to the basket," Jonty Rushforth, global editorial director for S&P Platts Global's oil and shipping price group, said at an industry conference.
"Far and away, Troll has received the most support."
Troll will add about 200,000 barrels per day, or 20 percent, to the basket of crude supplies underpinning the benchmark, Platts said. The move was in line with expectations after Platts said in December it was being considered.
Brent is used to set the price of billions of dollars of daily oil trade though a forward market for BFOE crude cargoes, swaps markets, physical benchmark dated Brent and Brent crude futures (LCOc1).
Troll, a light, sweet crude, is operated by Norwegian state producer Statoil (STL.OL), which also contributes to the Oseberg, Statfjord, Gullfaks, Grane and Asgard streams.
Statoil on Monday said it supported the move.
"We are pleased that Platts now has announced that Troll will be included," Statoil spokeswoman Elin Isaksen said in an email. "Troll will produce both oil and gas for a long time yet," she said in a separate email.
Platts announced the decision at its conference held a day before the start of the Energy Institute's IP Week, an annual gathering of the oil trading industry in London.
Some trade sources on Monday noted that Statoil's share of the production used to set the benchmark will rise -- a development Platts acknowledges.
"There is of course interest from the market in the ownership structure of the basket," Rushforth said at a media briefing. "It does mean that Statoil has a larger share than Shell and Total."
Even so, no single company would own more than a quarter of total production in the new basket, he said in a Platts video on the company's website.
Supply of the current four BFOE grades is normally around 1 million bpd, equal to just over 1 percent of world output.
The last change to the dated Brent benchmark was in 2007 when Platts added Ekofisk, a light, sweet crude. Oseberg and Forties were added in 2002.
In an earlier move to boost liquidity, Platts began to apply quality premiums to two better-quality crudes - Oseberg and Ekofisk - to encourage delivery of these into contracts.
There are no plans yet to apply one to Troll, said Platts, which will be sticking with the BFOE name.
Thomson Reuters competes with Platts in providing news and information to the oil market.
(Additional reporting by Amanda Cooper and Nerijus Adomaitis in Oslo; Editing by Mark Potter, Greg Mahlich)