Russia has slashed gas supplies to multiple European countries, worsening the energy crisis the continent was already facing before the war in Ukraine began.
Now, as winter approaches and major gas pipelines remain offline, European leaders are trying to secure alternative energy supplies.
They say Russian President Vladimir Putin is using energy for political leverage to swing the conflict in Ukraine in his favour.
Here are the key things you need to know.
Which countries has Russia cut gas supplies to?
Russia has cut off gas to Poland, Bulgaria, Finland, Denmark and Netherlands, saying they had refused to pay their bills in Russian currency.
Poland and Bulgaria openly denounced Moscow's payment rule, while Denmark's Prime Minister Mette Frederiksen called the move "a kind of blackmailing".
Russia has reduced supplies to six more countries.
Lithuania, Latvia and Estonia also mutually agreed in April to reject Russian gas in a show of solidarity with Ukraine.
Germany's gas supply was dialled back by two-thirds, with Russia blaming a part of natural-gas pipeline Nord Stream 1 being sent to Canada for maintenance and then not being returned.
The cut-off happened after the EU brought in heavy sanctions and members began supplying weapons to Ukraine.
What is the Nord Stream 1 pipeline?
Nord Stream 1 is the major European natural gas pipeline.
It runs under the Baltic Sea from Russia to Germany and is Germany's main source of Russian gas.
Three other pipelines bring Russian gas to Europe, but one through Poland and Belarus has been shut down.
Another through Ukraine and Slovakia is still bringing reduced amounts of gas despite the fighting, as is one through Turkey into Bulgaria.
Russia says the part sent to Canada hasn't been returned because of sanctions. Canada says it has sent back the part, but Germany won't say where it is.
How will the gas shortage affect Europe and the rest of the world?
Gas is used not just to heat homes, but also in processes most people will never see, including car manufacturing, making glass bottles and pasteurising milk and cheese.
Many companies can't switch immediately to other energy sources, and equipment holding molten metal or glass is ruined if the heat is switched off.
Europe is now scrambling to fill its gas storage before winter, when demand rises to keep homes warm and power plants running.
Europe's gas reserves are only 65 per cent full, compared to its goal of 80 per cent by November 1.
Right now, its plans is to use less gas to build storage, but high energy prices have already put the continent at greater risk of a recession.
If Russia completely cuts off the gas supply it could deal a heavy blow to the already troubled European economy.
Does the shortage mean people in Europe will freeze this winter?
Homes, schools and hospitals are unlikely to lose heat because governments are required to first impose rationing on businesses.
Officials may have to choose whether to sacrifice industries or hit consumers with even higher bills instead.
So what can Europe do about the shortage?
The EU is trying to switch to more expensive liquefied natural gas (LNG) from places like the US and Qatar, which comes by ship.
Germany is fast-tracking the construction of LNG import terminals but building them will take years.
And the world's LNG export facilities are already running at full capacity and LNG alone can't make up the gap.
Conservation and other energy sources are going to be key.
The EU has proposed member states cut their gas use by 15 per cent in the coming months, and officials want to impose mandatory reductions if there's a risk of a severe gas shortage or exceptionally high demand.
Countries are also scrambling to secure alternative gas and oil supplies.
Leaders in Italy, France and the EU are sealing deals with their counterparts in Algeria, Azerbaijan and the United Arab Emirates this week.
What does Vladimir Putin get out of cutting off the gas?
Since invading Ukraine, Russia's revenue from exporting oil and gas to Europe has doubled to $US95 billion ($138 billion).
The increase in Russia's energy revenue in just the past five months is three times what it would usually make over an entire winter.
So it's possible Mr Putin believes painful utility bills and a recession may undermine public support for Ukraine and swing negotiations in his favour, according to the International Energy Agency (IEA).
"It would be unwise to exclude the possibility that Russia could decide to forgo the revenue it gets from exporting gas to Europe in order to gain political leverage," IEA executive director Fatih Birol said.
Mr Putin says the amount of gas being pumped through Nord Stream 1 will fall further to about a fifth of its capacity.
AP/ABC
