Brent is based on the prices of four North Sea crude oils: Brent, Forties, Oseberg and Ekofisk. The export schedules for Brent and Oseberg both showed an increase in supplies.
More Forties oil is also expected in October as Nexen's Buzzard oilfield returns from maintenance. The number of 600,000-barrel Forties cargoes has fallen to 10 in September, before revisions, from 15 in August because of the work.
"It should be a bit more, more like the August programme," said a North Sea trader, referring to the Forties export schedule for October due to be released later on Thursday.
While October output is due to rise, a steady decline in North Sea output is raising doubts about the use of a dwindling source of supply as the main global oil benchmark. September's drop in supply boosted prices, in turn affecting the price of oil around the world.
Nexen started the maintenance at its Buzzard field on schedule this week and said it expected output to be shut down for several weeks before full production returns by mid-October.
September's supply of all four crudes that Brent is based on, known as BFOE, was originally planned to be 720,000 barrels per day (bpd), down from 774,000 bpd in August and a record low, according to Reuters data.
The Brent and Oseberg streams are due to provide a combined 50,000 bpd more oil in October, according to loading programmes.
Forties is the most important of the four for pricing because, as it is usually the lowest priced of the four, it sets the price of dated Brent. Dated Brent is used to price around two thirds of the world's oil supply.