The vast networks of pipelines that carry oil and natural gas around the globe bring more than just economic benefits. In some cases, they can foster better relations between countries. In other cases, they can strain ties.

It is a mathematical axiom that the shortest distance between two points is a straight line. But when building a pipeline, the shortest distance is sometimes sacrificed, and builders may be forced through an environmental or even political maze.

Robert Ebel, chair of the energy program at the Center for Strategic and International Studies, says that pipelines can drive wedges between nations, but they can also bring them closer together.

"Pipelines do bind nations together," he said. "The producer nations, the importer nations, the transit countries - all are interested in seeing to it that that pipeline is built on time, and that it operates without any problems because all would benefit. So there's that economic link, and there's a political link."

But the political link sometimes poses problems. One example is the proposal to build a pipeline to bring natural gas from the Caspian Sea to India, whose economic growth is fueling new demands for energy. One idea is to run the pipeline from Iran through Pakistan to India. But the U.S. government, currently at odds with Teheran over Iran's alleged nuclear ambitions, is keen not to give Iran any economic benefit.

Condoleezza Rice, left, is greeted by Indian FM Natwar Singh in New Delhi

Secretary of State Condoleezza Rice made that clear during a recent joint appearance before reporters with Indian Foreign Minister Natwar Singh.

"We have communicated to the Indian government our concerns about gas pipeline cooperation between Iran and India," she said. "I think our ambassador has made statements in that regard. And so those concerns are well-known to the Indian government."

But India does not share those concerns. Mr. Singh said India believes Iran will live up to its commitments under the Nuclear Non-Proliferation Treaty - a confidence not shared by the United States.

"We have traditional good relations with Iran," he said. "We expect Iran will fulfill all its obligations with regard to the NPT. We have no problems of any kind with Iran."

A pipeline bringing gas to India could also go through Afghanistan. But it would have to pass through Pakistan - India's neighbor and arch rival. At the recent World Economic Forum in Davos, Switzerland, Pakistani Prime Minister Shaukat Aziz said what he dubbed the "peace pipeline" will do much to heal the long-standing Indo-Pakistani rift.

"What we are trying to do is use this to meet our energy needs, but also to create interdependencies between countries because we firmly believe that if you create the linkages and interdependencies, you can push the peace process forward, much stronger," he said. "So if we do this pipeline and it does take off, I sincerely believe India-Pakistan relations will move forward in the right direction."

As Gal Luft, director of the Institute for Analysis of Global Security, points out, the economic benefits that transit countries like Pakistan or Afghanistan can enjoy also play into the political equations.

"Those countries make a lot of money by having the pipeline run through their territory. It's called transit fees, which could go all the way up to 20 or 30 or 40 cents per barrel, and sometimes even more," he said. "And for a lot of those countries, this provides a source of revenue, and therefore they would like to be involved in such projects."

For countries like Afghanistan and Pakistan, such transit revenues make a pipeline a lifeline to a battered economy.