Oil prices hit their lowest since 2003 on Monday, as the market braced for additional Iranian exports after the lifting of sanctions against the country over the weekend.
The United States and European Union on Saturday revoked sanctions that had cut Iran's oil exports by about 2 million barrels per day (bpd) since their pre-sanctions 2011 peak to little more than 1 million bpd.
Iran said on Sunday that it is ready to increase exports by 500,000 bpd. Iran is the world's seventh-largest oil producer.
Worries about Iran's return to an already oversupplied oil market drove down Brent crude to $27.67 a barrel early on Monday, its lowest since 2003. The benchmark was at $28.59 by 4:21 a.m. ET, down 38 cents from its settlement on Friday.
U.S. crude was down 38 cents at $29.04 a barrel, not far from a 2003 low of $28.36 hit earlier in the session.
U.S. crude oil prices have trended down for a year and a half, and have fallen almost 40 percent in just the past three months. That compares with a high of over $100 a barrel in the summer of 2014, and close to $150 per barrel before the U.S. recession.
Falling crude prices have led to lower prices for gasoline, diesel, jet fuel and heating oil. This has helped boost consumer spirits and encourage spending, but may also have slowed the overall recovery of the U.S. economy last year as major energy companies slash investments and jobs.
The return of Iran to global energy markets created tremors even before the first trade was made. Saudi Arabia's stock market plunged more than 5 percent Sunday. Saudi Arabia is the biggest oil producer within OPEC, the oil cartel with waning influence to which Iran also belongs.
Iran has at least a dozen Very Large Crude Carrier super-tankers filled and in place to sell into the market, and traders are betting that oil prices will drop again.