The falls came after both crude benchmarks early last week hit highs last seen in 2015, but traders said the market had lost some momentum since then.
Speaking at the Abu Dhabi International Petroleum Exhibition Conference (ADIPEC), al-Mazroui said: "My prediction is OPEC will continue to do what it takes to rebalance the market", CNBC reported.
OPEC members are reportedly forming a consensus around extending by nine months their production-cutting deal with other crude exporters, through the end of 2018.
OPEC and other non-OPEC producers will meet on November 30 in Vienna to decide on oil output policy.
Australia v Honduras: Tim Cahill ready to lead Socceroos to Russian Federation
The players were eventually allowed to train on the pitch after wearing bibs and pullovers that hid the logo. It just takes some of the merit away from the fair play and the sporting event that will be held tomorrow".
The exporters reached the deal last December and have already extended the agreement through March 2018.
Throughout the week, prices were also bolstered by rising global demand data and expectations that OPEC and other producing countries will extend a deal to cut output.
In May, Opec producers agreed to extend production cuts for a period of nine months until March, but stuck to production cuts of 1.2 million bpd agreed in November past year.
Oil prices settled mixed on Monday as geopolitical tension in Middle East offsets rising US output.
HTC Vive Focus standalone VR headset launched
Somehow he ended up in London, where he had the golden opportunity to buy a then senior editor a pint of lager, and here we are. No launch price or date has been announced , though developers can sign up for a development kit on HTC's Vive Focus page .
On the supply side, tensions in the Middle East raised the prospect of disruptions, traders said, adding it was unclear whether a strong quake that hit Iran and Iraq on Sunday had affected the region's oil production.
The price of Iran's light crude oil in the week ended on November 3 rose $2.59 to stand at $60.04 per barrel, IRIB reported on Sunday.
Bahrain said at the weekend that an explosion that caused a fire at its main oil pipeline on Friday was caused by sabotage, linking the attack to Iran, which denied any role.
Moon, Russian PM agree to strengthen cooperation on N
President Moon Jae-in and Chinese President Xi Jinping agreed to hold a third bilateral summit next month in China. Xi noted his meeting with the South Korean leader marked a turnaround in South Korea-China relations.