In 2013, Europe, Turkey, Norway, Switzerland, and the non-EU Balkan states consumed 18.7 trillion cubic feet of natural gas, while Russia supplied 30 percent of this volume.

The U.S. Energy Information Administration (EIA) estimates that 16 percent of the total natural gas consumed in Europe passed through Ukraine's pipeline network, based on data reported by Gazprom and Eastern Bloc Energy.

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Two major pipeline systems carry Russian gas through Ukraine to Western Europe—the Bratstvo (Brotherhood) and Soyuz (Union) pipelines.

The Bratstvo pipeline is Russia's largest pipeline to Europe. It crosses from Ukraine to Slovakia and splits in two to supply northern and southern European countries.

The Soyuz pipeline links Russian pipelines to natural gas networks in Central Asia and supplies additional volumes to central and northern Europe.

A third major pipeline through Ukraine (Trans-Balkan) delivers Russian natural gas to the Balkan countries and Turkey.

To read the full EIA report on this story, go here