US forces are struggling to contain a fire and maintain security on Iraq's main oil export pipeline following two attacks by saboteurs.
Nearly half Iraq's oil comes from the Kirkuk fields
US Army engineers are using helicopters to try to control the flames with water, but officials have already warned it could take weeks before the pipeline is working again.
Meanwhile, the first batch of more than 6,500 guards who will be used along the pipeline have started training.
They will be joining more than 5,000 Iraqis already watching the 1,000-kilometre (600-mile) pipeline to Turkey.
The blaze has fuelled fears of a determined campaign by saboteurs to disrupt the country's key infrastructure.
In a spate of attacks at the weekend, two fires were started on a northern section of the oil pipeline to the Turkish port of Ceyhan and a water main was blown up in Baghdad.
Now Iraq stands to lose $7m a day in revenue, says the BBC's Susannah Price in Baghdad.
Experts warn that unless Iraq can ensure a constant supply of its oil, customers may go elsewhere.
Oil traders say crude stocks remain plentiful so although prices rose on Monday after the pipeline attack, dramatic or sustained price increases remain unlikely.
The price of Brent crude oil for delivery in September - set in London and a benchmark for oil prices worldwide - rose 36 US cents to $29.17 a barrel.
US light crude, the main benchmark on Wall Street, added 27 cents to $31.32.
Brent crude, which acts as a benchmark for oil prices worldwide, was 35 cents a barrel up at $29.16.
Gasoline for September delivery was trading at $1 a gallon, having touched $1.25 last week, its highest level since the Iraq war.
Recovery at risk
The contract to provide additional guards has been awarded to an international security company already working in Iraq.
The guards - expected to be mostly Iraqis - will include some of those carrying out similar work along the pipeline and members of local tribes.
Our correspondent says it is a massive task and questions are already being asked about the level of commitment such guards might have in the face of an attack.
The US governor of Iraq, Paul Bremer, has already warned that Iraq's economic recovery will be hit if the country's infrastructure continues to suffer sabotage attacks - blamed on supporters of the former Saddam Hussein regime.
During the weekend, an attack on a water main left 300,000 people in Baghdad without water, while a mortar attack on a prison killed six Iraqis and injured 59 others.
Elsewhere, a fire in a sewage treatment plant was reported.
"The irony is that Iraq is a rich country that is temporarily poor," Mr Bremer told the meeting of a committee coordinating foreign aid for Iraq.
The damaged pipeline carries oil from the giant oilfields at Kirkuk, which accounts for 40% of Iraq's oil production, to a Turkish terminal at Ceyhan.
The pipeline was disabled on Friday when a fire broke out at a section in Bajii, north of Tikrit, the home town of ousted Iraqi leader Saddam Hussein.
The fire came just two days after the pipeline had reopened for the first time since the invasion of Iraq in March.
Officials said it appeared the fire had been started deliberately.
"We believe at this stage it was an explosive device planted on the pipeline," said the US-appointed interim oil minister in Iraq, Thamir Ghadban, following the blast.