One of the world’s greatest civil engineering projects, the $8 billion Trans-Alaska Pipeline System (TAPS) carries crude oil 800 miles south from Prudhoe Bay on the Arctic Ocean to a pipeline terminus at Port Valdez. Built between 1975 and 1977, the pipeline at the time was the largest and most expensive privately funded construction project ever undertaken.

The first tanker load of oil shipped out of Valdez in August 1977. Today, Alyeska Pipeline Service Company, a consortium of oil companies that includes BP, Phillips, ExxonMobil, Unocal, Williams and Amerada Hess, owns and operates the pipeline. Since starting up, TAPS has successfully transported more than 14 billion barrels of oil.

The 48-inch-diameter pipeline winds its way through three major mountain ranges, with its highest point at 4,700-foot Atigun Pass in the Brooks Range, 170 miles south of Prudhoe Bay. Along the Richardson Highway, the pipeline crests the Alaska Range at 3,420 feet at Isabel Pass, before descending into the Copper River Basin. It crosses the Chugach Mountains at Thompson Pass and descends through the Keystone Canyon to Valdez, where gravity feeds it into tanks or directly into oil tankers at the marine terminal.

Because of varying soil conditions along its route, the pipeline runs both above and below ground. Where the warm oil might cause permafrost to thaw and erode, a factor along 75 percent of the length, the pipeline goes above ground. Where the frozen ground is mostly well-drained gravel or solid rock and thawing is not a problem, the line goes underground. The zigzag pattern of many of the above-ground sections allows for pipe expansion or contraction, due to temperature changes or movement caused by other forces, such as earthquakes.

It takes 8.6 days for crude oil to flow from Prudhoe Bay to Valdez, with more than 9 million barrels worth of oil in the pipeline at any given time.