International oil prices fell after US officials voiced optimism that shipping through the Strait of Hormuz could resume.
Brent crude dropped by about 5% to below $80 a barrel.
US West Texas Intermediate crude fell by more than 5% to about $76 a barrel.
Both benchmarks were at their lowest levels since 13 July.
US Secretary of State Marco Rubio said discussions involving Iran and Oman on increasing shipping through the strait had made progress.
Rubio said a final agreement had not yet been reached, but he expected one soon.
US Treasury Secretary Scott Bessent said an agreement to reopen the strait could be reached within days and described the intended arrangement as allowing free passage.
Iran said it was not in talks with the United States and had no plan to begin such talks.
An Iranian Foreign Ministry spokesperson said discussions with Oman on a new shipping mechanism through the strait had been positive.
Qatar said it was continuing diplomatic efforts with other mediators but that no direct Washington-Tehran talks were scheduled.
The terms and structure of any possible shipping agreement had not been publicly detailed.
Before the conflict that began in late February, the strait carried about one-fifth of global daily oil and liquefied natural gas supplies.