Oil held losses near $67 a barrel on speculation that an escalating trade dispute between the US and China will dampen global growth at a time when American crude inventories are growing.
WTI had traded at $69.61 per barrel on Monday, Oct. 22, before it fell sharply during the past week.
There has been concern that in the context of the USA sanctions against Iran, which are now set to take effect on November 4, Saudi Arabia could cut crude supply in retaliation for potential sanctions against it over the disappearance of Saudi journalist Jamal Khashoggi.
Even with USA sanctions on Iranian exports due to begin on November 4, oil prices have fallen roughly $10/Bbl since four-year highs were hit in early October. A speculative long position reflects a view that prices will increase.
Trump's goal by exerting energy sanctions on Iran was to minimize the country's sources of income in the current economic war against Iran, he said.
In other related news on Monday, the U.S. Energy Information Administration's latest analysis of planned refinery outages for the fourth quarter of 2018 finds that planned outages in the United States are not likely to cause a shortfall in the supply of petroleum products-including gasoline, jet fuel and distillate fuel relative to expected demand, either nationally or within any U.S. region.
The sanctions have triggered a black-market fueled by Iranian tankers - or "ghost ships" - that dismantle their vessel tracking systems, according to regional observers, making it extremely hard to estimate how much Iranian oil is on the market at any given moment.
However, U.S. equities rebounded strongly on Thursday, with the Nasdaq Composite Index jumping about 3 percent in late trading, soothing anxious investors to some extent.
"Iran used to sell its oil at $30 per barrel but is now selling it at $80 per barrel", Jahangiri added.
The U.S. reimposed other non-oil sanctions in August, but next week's tranche is expected to have the greatest economic effect. However, oil futures lost about 2.4% in the week, settling lower for a second straight week.
Prices were pressured as USA inventories were expected to rise for a sixth straight week as other top producers Saudi Arabia and Russian Federation signaled potential output increases.
In the coming weeks, traders keep a close eye on USA sanctions on Iranian crude exports.
The United States has 875 operating oil drilling rigs in this week, adding two more from the previous week, according to data issued by oil service company Baker Hughes on Friday.
Investors awaited industry data on USA crude inventories due to be released at 4:30 p.m. EDT on Tuesday.