As of noon on Monday, Brent crude was trading at $57.57 per barrel, an increase of $1.15 from Friday's trading price of $56.42.
"London Brent crude delivery for November slipped 8¢ to $56.78 a barrel, while the U.S. crude fell roughly 15¢ to a value of $50.51 per barrel".
Futures rose as much as 1.4 percent in London to the highest since February 2.
Rising production from the two exempt OPEC members-chiefly from Libya-has indeed slowed down the oil price improvement that OPEC targeted with its agreement. A gathering in Vienna last week between OPEC and its allies ended with no decision on an extension or deepening of the cuts beyond the first quarter of 2018, while the potential revival of USA shale production is also weighing on the outlook for prices.
Oil has advanced this month on forecasts of strong demand and as U.S. Gulf Coast refineries resume operations after Hurricane Harvey.
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"If this boycott call proves successful, a good 500,000 fewer barrels of crude oil per day would reach the market", Commerzbank said in a note. "At the same time, without any firm plans for after March 2018, discussions will start about the end game of the OPEC deal and erode confidence".
Elsewhere, in the US, market participants mulled over data showing the number of oil rigs continued to decline, suggesting a possible tightening in domestic production.
Iraq's goal to boost production capacity to 5 million barrels a day won't affect markets and not all new output will be exported, Oil Minister Jabbar Al-Luaibi said in Baghdad.
"We're seeing more and more evidence that it's not the worldwide oil companies, it's not the independent oil companies that are lagging new investments, but it's OPEC countries lagging, particularly those five", he said.
But Britain's economy is expected to suffer more generally should prices continue to rise towards $60 a barrel.