Oil prices fell around 2% during Friday's Asian trade, on track for steep weekly losses as improving crude shipments through the Strait of Hormuz eased supply concerns, despite a reported attack on a cargo vessel near Oman that renewed security fears in the region.
By 2:50 pm AEST (4:50 am GMT), Brent crude futures for September delivery had fallen $1.40, or 1.9%, to US$74.10 a barrel, while US West Texas Intermediate crude declined $1.48, or 2.1%, to US$70.44 a barrel.
Both benchmark contracts had rallied more than 2% on Thursday after a cargo vessel was struck by an unidentified projectile near Oman, prompting the United Nations' International Maritime Organization (IMO) to suspend its voluntary evacuation programme for stranded ships.
ANZ analysts said uncertainty surrounding the incident had temporarily revived concerns over shipping security in the Strait of Hormuz.
"The Wall Street Journal reported that it was an attack by Iran, although there has been no confirmation. This comes as several commercial ships turned around while attempting to transit the strait, raising fresh doubts over the continued recovery of oil supply that had emerged following the reopening of the key waterway under the ceasefire agreement signed last week.
"Ship tracking data has shown that Persian Gulf oil was moving through Hormuz at the fastest pace since the Middle East conflict began. Producers were also preparing to restart production.
"Qatar issued its first tender to sell crude since the conflict began, while Saudi Arabian-owned ships are heading for the major Ras Tanura oil terminal."
Despite Thursday's rebound, both Brent and WTI were on course to post weekly losses of about 8%.
Market sentiment was supported by data showing crude shipments through the Strait of Hormuz had climbed to their highest level since the U.S.-Israeli conflict with Iran began in February after a ceasefire agreement reopened the vital waterway.
However, traders remained cautious over the durability of the reopening and the risk of further disruptions.
Even so, overall shipping volumes remain well below the average of around 125 vessels per day that transited the strait before the conflict erupted on 28 February.
ING commodities strategists said the recent increase in shipping activity largely reflected vessels that had been stranded during the conflict rather than a full recovery in normal trade flows.
"However, much of the increase reflects previously stranded vessels leaving the Persian Gulf. Vessel flows into the Gulf remain much more modest. It suggests that once stranded vessels have moved out, we could see a pullback in flows.
"Also, the latest strike on a vessel will likely slow traffic, with the International Maritime Organisation suspending its evacuation plan for stranded ships."
Elsewhere, earthquakes in Venezuela added another layer of uncertainty to global oil markets.
Initial assessments indicated the country's major oilfields, refineries, pipelines and export terminals had suffered only limited damage, as most production infrastructure is located well away from the hardest-hit regions.
