Oil prices slipped further on Friday, heading for a weekly loss of more than 6 per cent, after a report that Washington has granted several countries sanction waivers allowing them to continue to import Iranian crude.
Brent crude oil was down 10 cents a barrel at $72.79 by 1400 GMT. The contract has fallen by almost 12 per cent since the beginning of October when it reached its highest since 2014.
US light crude weakened by 30 cents to $63.39, down more than 13 per cent since hitting four-year highs a month ago.
Investors are concerned about the prospects for oil supply when new US sanctions are implemented against Iran on Monday.
Washington has said it aims eventually to stop all Iranian oil exports but has granted several countries waivers on sanctions, allowing them to continue imports for a while.
The US government has agreed to let eight countries, including South Korea, Japan and India, keep buying Iranian oil after it reimposes the sanctions, Bloomberg reported on Friday, citing a US official.
"Oil prices look to remain under pressure, as fears of global oversupply have returned with a vengeance," said Ashley Kelty, oil and gas research analyst at Cantor Fitzgerald Europe.
A list of all countries receiving US waivers allowing them to import Iranian oil is expected to be released officially on Monday, industry sources say. Despite these efforts, waivers are likely to be only temporary.
Goldman Sachs said it expected Iran's crude oil exports to fall to 1.15 million barrels per day (bpd) by the end of the year, down from about 2.5 million bpd in mid-2018.
World oil production has been rising significantly in the past two months. Russian Energy Ministry data showed on Friday that the country pumped 11.41 million bpd of crude in October, a 30-year high.
The Organization of the Petroleum Exporting Countries boosted oil production in October to 33.31 million bpd, up 390,000 bpd and the highest by OPEC since 2016.
And in the United States, crude production is now comfortably above 11 million bpd, putting the United States in a neck and neck race with Russia for the title of top producer.
"US production up, Russian production up, OPEC production up. Now we have eight countries that are going to get waivers," Mark Scullion, futures and options broker at Eclipse International in New York, told the Reuters Global Oil Forum.
"Even though we've had a whole month of lower oil prices, I'm still looking for a bit more downside."