Trans-Alaska Pipeline, pipeline that connects the oil fields of Prudhoe Bay in northern Alaska, U.S., with the harbour at Valdez, 800 miles (1,300 km) to the south.

The discovery of oil on Alaska’s North Slope in 1968 spurred the creation of a safe and efficient way to bring those reserves to market. Atlantic Richfield Company, British Petroleum (now BP PLC), and Humble Oil (a subsidiary of Exxon Corporation) agreed to build a pipeline that would connect the North Slope to Valdez, an ice-free port on Prince William Sound (an embayment of the Gulf of Alaska). The movement of oil through the 48-inch (1.2-metre) pipe would be boosted by pumping stations situated along its length, ensuring a constant flow at roughly 4 miles (6 km) per hour. At this rate, oil would complete the journey from Prudhoe Bay to Valdez in about nine days.

A series of environmental impact studies were commissioned, and their results led to changes in the pipeline’s design—notably that about half of the pipeline would be elevated to prevent the heated oil in it from thawing the permafrost and to allow wildlife to pass more easily under it. Portions of the pipeline were also to be buried where necessary, in part to facilitate the movement of wildlife. Other special construction measures included installing devices to dissipate heat buildup in permafrost ground around pipeline-support trestles and building bridges for the pipeline across rivers and streams to avoid burying the pipeline at those locations.

On Nov. 16, 1973, Pres. Richard M. Nixon signed the Trans-Alaska Pipeline Authorization Act into law, and much of the next year was spent building access roads along the proposed route (the Dalton Highway now parallels the entire pipeline). Construction on the $8 billion pipeline began on March 27, 1975. The final weld was completed at Pumping Station 3, near Atigun Pass, on May 31, 1977, and oil began to flow through the pipeline on June 20. However, a series of mechanical problems halted the pipeline’s operation, and oil did not arrive at Valdez until July 28.

In spite of these difficulties, production continued, and the pipeline moved its billionth barrel of oil in early 1980. Attention was focused on the southern terminus of the pipeline in 1989 when the tanker Exxon Valdez ran aground in Prince William Sound. Images of oil-slicked sea birds and otters provided stark examples of the dangers of an oil spill in the Arctic. Though of a smaller scale than the Exxon Valdez disaster, the largest spill in the history of the pipeline occurred in 2006 when a transit pipe at BP’s Prudhoe Bay facility ruptured. More than a quarter million gallons (one million litres) of oil spilled onto the tundra, and Prudhoe Bay production was halved as engineers spent months replacing corroded pipe.