The countries are now the two key oil supply concerns globally that supported the oil price rally in recent weeks, before Saudi Arabia and Russian Federation hinted at discussions that they were considering reversing some of the cuts to offset production losses and "ease market and consumer anxiety".
Brent crude futures, the global benchmark for oil prices, were at $76.79 per barrel at 0654 GMT, down 53 cents, or 0.7 percent, from their last close.
US West Texas Intermediate (WTI) crude futures peaked at $72.30 a barrel, also its highest.
JP Morgan cut its 2018 crude forecast for WTI by $3 to $62.20 a barrel, traders said.
Crude-oil futures finished slightly lower on Friday and registered a marginal decline for the week as worries over potential supply shortages in South America and the Middle East knocked prices around throughout the five-session period. The bank said geopolitical tensions and lingering risks of supply disruptions may push prices higher during the second half 2018, it expects prices will head lower late in the year, and remain capped in 2019.
Further weighing on prices has been rising US output, which hit another record last week at 10.8 million bpd.
Venezuelan state-run oil company PDVSA has completed its first ship-to-ship (STS) transfer created to ease a severe bottleneck of tankers around its main crude ports, according to sources close to the operation and Reuters vessel tracking data.
May shipments were 39.05 million tonnes, or 9.2 million barrels per day (bpd).
OPEC and a number of non-member countries agreed at the end of 2016 in Vienna to reduce their oil production by a total of 1.8 million barrels per day from October 2016.
Algerian Energy Minister Mustapha Guitouni said on state radio: "What matters to us is that there is a balance between supply and demand to ensure the stability of the oil markets".
Despite Friday's decline, Brent remains more than 15 percent above its level at the start of the year.
Among them are the political and economic instability in Venezuela and speculations that Saudi Arabia and Russian Federation are ready to exit the supply cuts agreed on by members and non-members of Organisation of Petroleum Exporting Countries (OPEC).
Reuters reports that the containers are waiting to load more than 24 million barrels of crude.
OPEC member Venezuela, threatened with US sanctions in the midst of an economic crisis, is almost a month behind delivering crude to customers from its main export terminals, according to shipping data.
Iran has called on Opec to discuss what it called "illegal" sanctions at the next meeting on June 22, which is due to debate production policies.
Headlines on OPEC members' plans for the meeting later this month will lead to volatile market swings, said Tariq Zahir, managing member of Tyche Capital Advisors in NY. "I believe that the help of the European Union helps us. the level of our oil exports will not change", Zangeneh said.