Two OPEC+ delegates, who could only comment anonymously because of the sensitivity of the talks, told CNBC that the coalition has sharpened its focus on the conformity of its members. Undercompliance has been a repeat bane of the OPEC+ alliance,

Expectations that the OPEC and its allies will start unwinding voluntary output curbs of 2.2 million barrels a day starting from December is adding to market nervousness.

OPEC+ is set to go ahead with a December oil output increase as its impact will be small should a plan for some members to make larger cuts to compensate for overproduction be delivered in September and later months,

Separately, the Organization of Petroleum Exporting Countries (OPEC), and its allies, a group known as OPEC+, are currently cutting oil output by a total of 5.86 million bpd but it plans to reverse 180,000 bpd of those cuts in December.

The output increase in December is not about regaining market share, it is about a small number of countries phasing out their voluntary output cuts, one of the OPEC+ sources said

Oil prices fell more than 3% on Thursday on a Financial Times report that Saudi Arabia, the world's top crude exporter, will give up its $100 price target in preparation for raising output, along with OPEC members and allies in December.