Brent crude futures climbed above $91 a barrel on Tuesday, extending gains for a third consecutive session as fading prospects for a new U.S.-Iran agreement raised concerns about prolonged disruption to oil supplies.
Brent rose 89 cents, or about 1%, to $91.76 a barrel, its highest level since July 30, while U.S. West Texas Intermediate crude gained $1.05 to $85.55 a barrel.
The gains came after U.S. President Donald Trump ruled out extending an interim agreement with Iran, while Tehran said it would adopt a more offensive military posture if diplomacy fails. The 60-day memorandum agreed in June expired on Monday without a longer-term peace deal.
The uncertainty has renewed concerns over the Strait of Hormuz, through which a significant share of global oil supplies normally passes. Tanker traffic through the waterway remains severely restricted, while attacks on vessels have added to fears of further supply disruptions.
Iran and Oman are separately discussing arrangements for navigation through the strait, but Washington has not been part of those talks. Any agreement that does not guarantee unrestricted passage is unlikely to resolve concerns in global oil markets, analysts say.
Oil prices have also been supported by efforts by Middle Eastern producers and traders to maintain exports through alternative routes and covert shipments, helping to cushion some of the impact of the disruption around Hormuz.
The latest rise follows a more than $2 gain in Brent on Monday, when the benchmark settled at $90.87 a barrel as investors reacted to stalled peace efforts and growing supply risks.
With diplomatic efforts showing little progress, the market is increasingly focused on how long restrictions around the Strait of Hormuz will last and whether further military escalation could tighten global crude supplies.
