From the air, the Caño Limón pipeline is invisible. The 480-mile tube is buried 6 feet below ground, but its route through the rolling Colombian prairie is marked by a swathe of black oil slicks and burned ground, the result of repeated bomb attacks by leftist rebels.
The pipeline, which links the oil field near the border with Venezuela to a port on Colombia's Caribbean coast, has been punctured so many times in the last 16 years that locals call it "the flute." Some 2.9 million barrels of crude oil have leaked into the soil and rivers - about 11 times the amount spilled in the 1989 Exxon Valdez disaster.
Now the US government is seeking Congressional approval for $98 million to provide equipment and training for a new Colombian Army brigade to guard the oil duct. If approved, it would mark a major shift in US policy, allowing direct support for counterinsurgency operations against guerrilla saboteurs.
Oil is Colombia's biggest foreign-currency earner, and US officials say the aid is essential for the Colombian government, a key ally in the US war on drugs. But critics say it is still unclear whose interests are being served.
Last year, 170 bomb attacks disabled the pipeline for most of the year. It cost Occidental Petroleum, which runs the field, $75 million in profits - and cost the government $430 million in oil revenue.
"We're talking about something which is fundamental for the economy of the country. Of course there is a US interest, but [with the attacks] it is Colombia which is losing out," says an Occidental spokesman.
As the country spirals deeper into civil war, some fear that the aid package signals that the Bush government is more concerned with protecting the interests of American companies than in helping to end a 38-year conflict.
"It's a way of saying that US interests trump everything else. There are real and legitimate reasons to protect the pipeline, but given all that Colombia needs, is this really a priority?" says Robin Kirk, a Colombia analyst at Human Rights Watch.
Most of the rebel attacks occur in the first 75 miles, where the duct passes through the wild frontier zone of Arauca state, which has been a rebel stronghold for decades.
Colombia's two largest guerrilla armies, the Revolutionary Armed Forces of Colombia (FARC) and the National Liberation Army (ELN), oppose foreign involvement in the nation's oil industry and, according to the Colombian military, the rebels hope that the pipeline attacks will weaken the government by depriving it of foreign earnings.
"The intensity of the attacks shows that the pipeline is a fundamental strategic target," says Brig. Gen. Carlos Lemus, commander of the 18th Brigade, and the man who will oversee the new unit if and when it is formed.
The brigade's badge shows a soldier guarding an oil well under a blazing prairie sun, and according to General Lemus, two-thirds of Colombia's troops are already dedicated to defending the oil infrastructure. But the Army is incapable of protecting the entire pipeline, which can be punctured with a relatively small explosive.
"We need mobility and the capacity to react fast. With the right equipment we could defend it, but our resources are limited," says Lemus.
The general doesn't even have his own helicopter, and with the roads often blockaded by guerrillas, Lemus must cadge a ride on an Occidental helicopter to visit troops along the pipeline. Under an agreement with the government, Occidental provides "nonlethal" aid to the Army such as fuel, food, and transport, but Lemus believes it could do more.
"I think that the company hasn't done enough to apply modern technology. We've been asking them to install some kind of early-warning system with sensors. At the moment, the only sensors are our soldiers," he says.
Troops on motorbikes patrol the access roads around the Occidental compound, while a Colombian Army surveillance plane circles overhead. This year, the troops have foiled some 17 attacks already, but according to one officer, the region's problem cannot be solved by military means alone.
"Even if we had the entire Colombian Army guarding the pipeline, with a soldier every 500 meters, we couldn't prevent every attack," says Maj. Edgar Delgado, commander of the Army base at the oilfield. "We don't need more aircraft or more weapons," he says. "The [military] aid should come with progress - education, health clinics, and roads."
Before the first prospectors struck oil, Arauca was a sparsely populated cattle-ranching region, mostly ignored by the central government. Royalty payments and company handouts brought electricity, roads, and some jobs, but the oil boom also caused a population explosion, inflation, and the decline of local agriculture.
Local officials say that most of the profits have been siphoned off by corrupt politicians. The state capital, also called Arauca, is dotted with costly white-elephant building projects such as a velodrome, which was used just once and is now flooded and abandoned.
"Whenever there is a boom, people think it will solve all their problems," says Oscar García, president of the local chapter of the Colombian oilworkers union. "We had very big expectations, but we weren't prepared to handle this much money."
Ironically, the rebels have grown rich on oil money, using threats and intimidation to force officials to use companies with guerrilla ties, and regularly charging a 5 percent "tax" on every government contract.
Local government depends on royalties to meet its budget, and so every bomb attack means less money for the region's schools and hospitals, says Arauca Mayor Jorge Cedeño. But unemployment and the thin state presence mean that the guerrillas still offer an alternative for the disaffected rural poor.
"If they have to reinforce security, let them do it, but there must also be social development. If we don't solve the social problems, the war will continue."