Russian gas exports to Europe play a key role in the Ukraine crisis ...

As the U.S. and its allies work to present a unified front to avert a Russian invasion of Ukraine, worries about Europe's energy reliance on Russia threaten to complicate the response.As much as 40% of the continent's natural gas is supplied by Russia — prompting fears about what might happen if Moscow moves to cut off some or all of that supply.U.S. officials have warned that Russia has nearly enough military power deployed along Ukraine's borders to stage a full-scale invasion of the country.But even as world leaders crisscross the continent for diplomatic meetings and the U.S. and NATO move troops around Eastern Europe, the European energy piece is in the spotlight.Read on to understand why.In short, many countries in Europe are dependent on Russia for imports of natural gas and, to a lesser extent, oil.Foremost among them is Germany, Europe's largest economy, a key ally of the United States and a historically important participant in negotiations about Ukraine.No country buys more natural gas from Russia than Germany, which depends on the fuel to help heat homes in winter and operate factories.German Chancellor Olaf Scholz visited the White House this week, where talks with President Biden about a Russia-to-Germany pipeline called Nord Stream 2 were front and center. Nord Stream 2, owned by Russian energy company Gazprom, is to transport Russian natural gas from Russia to Germany, but President Biden has said the pipeline will not go forward if Russia invades Ukraine. Nord Stream 2, owned by Russian energy company Gazprom, is to transport Russian natural gas from Russia to Germany, but President Biden has said the pipeline will not go forward if Russia invades Ukraine.The Biden administration has said the U.S. will prevent Nord Stream 2 from coming online if Russia invades Ukraine. (Its reliance on Ukraine-based pipelines is part of the reason for its interest in Nord Stream 2.)With supply drastically affected, Europe's already-high energy prices would likely skyrocket."If we will get additional volumes from Norway and from Azerbaijan and from Qatar and from the United States, then we can build up a scenario how to handle the situation that is theoretically possible if we have full disruption of gas flows from Russia," said European Commissioner for Energy Kadri Simson, speaking at a news conference on Tuesday.One short-term solution is importing liquefied natural gas from countries like Qatar and the U.S. The U.S. has dramatically increased its exports of LNG to Europe in recent years.