Also known as oil sands, tar sands are grains of sand intermixed with bitumen (heavy, black, asphalt-like oil). The oil locked up in tar sands requires drastic efforts to extract, and the result is a particularly dirty form of energy production.

How are tar sands extracted?

There are two primary ways to extract oil from tar sands:

1. The deposits are mined, the oil removed, and the sands returned to the pit or discarded elsewhere.
2. In situ recovery is used for deeper deposits -- usually more than 250 feet, and frequently more 1,000 feet below the surface. In-place recovery involves injecting substances to heat up the sands, making the bitumen fluid enough to be pumped out of the ground.

After the heavy oils and bitumen are extracted, they are thinned using another petroleum product, enabling the final product to flow through a pipeline. Further processing also occurs in order to produce a higher quality crude oil.

Where are tar sands found?

Tar sands are currently being mined extensively in the Athabasca oil sands in northeastern Alberta, Canada. In the U.S., small, unexploited tar sands deposits are located in Utah, Kentucky, Kansas, Missouri, California, and New Mexico.

Why are tar sands dirty?

Each stage of tar sand and oil shale processing and upgrading requires the use of significant quantities of energy -- mainly from burning fossil fuels -- and significant harm to the environment.

Mining for tar sands, for example, requires stripping thousands of acres of fertile ground and using massive amounts of water. In fact, it has been estimated that once the tar sands project in Alberta, Canada is completed, it will have devastated an area the size of Florida and consumed millions of gallons of fresh water.

Oil derived from tar sands can have serious impacts on climate even before it is burned -- estimates show that extraction and processing of tar sands generates between 5 to 10 times more carbon dioxide emissions than conventional oil. In other words, fully developing the Alberta tar sands could mean the battle to limit global warming will be lost before it ever really begins. Processing and refining the oil also generates major amounts of toxic and carcinogenic (cancer-causing) contaminants, which can spread for miles over human and animal habitats.

For More Information

• NDE: tar sands and climate change

• NDE: how tar sands oil affects the United States

• Alberta Energy:

  Alberta government energy agency's discussions include the Alberta government's policy on tar sands development.

• Boreal Songbird Initiative:

  Canadian birding group's links to Canadian Broadcasting Corporation's investigations of community concerns and environmental risks.

• Environmental News Service:

  Environmental news group's article voices the U.S. Conference of Mayor's opposition to "dirty fuels".

• The Guardian:

  British news agency's video drills the industry for answers on their poor environmental performance.

• The Pembina Institute:

  Sustainability advocacy group's discussions include in depth reports on the performance of tar sand industries and the Canadian Government.

• WWF-UK:

  Unconventional Oil -- scraping the bottom of the barrel?

Tag it:

?