Brent crude fell 60 cents to settle at $51.81 a barrel, while U.S. West Texas Intermediate crude slipped 61 cents to settle at $50.18 a barrel.
VIENNA: Saudi Arabia has told its U.S. and European customers it will reduce oil deliveries from January, as Russia said it was confident non-OPEC producers would fully join OPEC's output limits on Saturday in the first such move since 2001.
OPEC will meet non-OPEC producing countries in Vienna on Saturday, hoping non-OPEC will commit to cutting 600,000 barrels per day after its own members agreed to cut 1.2 million bpd last week.
OPEC sources said nine non-OPEC countries were set to join the meeting: Azerbaijan, Kazakhstan, Oman, Mexico, Russia, Sudan, South Sudan, Bahrain and Malaysia. Bolivia may also attend the talks, according to an OPEC source.
Saudi Arabia's energy minister Khalid al-Falih said he was "very optimistic" about the Saturday meeting.
"We will know the exact numbers tomorrow but I am expecting about 10 to 11 (non-OPEC) countries to be on the final declaration with specific numbers," he told reporters upon arriving to Vienna.
So far only Russia and Oman have pledged cuts, with one OPEC source saying Mexico could also contribute as much as 150,000 bpd.
In contrast, Kazakhstan plans to boost output in 2017 as it launches the long-delayed Kashagan project.
Saudi Arabia told the customers about lower supplies in line with the output reduction agreed by the Organization of the Petroleum Exporting Countries last week, according to a Gulf oil industry source familiar with Saudi oil policy.
