With the arrival of winter in Europe and energy prices soaring, tensions are running high over the provision of gas from Russia — especially through the Yamal-Europe pipeline that runs through Poland and Belarus.
But the Yamal pipeline is just one part of a complex gas infrastructure network shaped not only by energy needs but also wider economic interests and politics, including strife between Russia and Ukraine.
The pipeline, opened in 1994, runs over 2,000 kilometers (1,242 miles) to Germany from the city of Torjok in central Russia, transiting through Belarus and Poland.
It delivers 30 billion cubic meters of gas to Europe each year, making it one of the most important vehicles for the provision of Russian gas to the continent.
Russia sells Germany gas at a cheaper rate than it does to Poland, in part to make up for the higher transit fees through the longer delivery distance.
But this means that it is more cost efficient for Poland to buy Russian gas from Germany.
Some of the gas sold by German traders to Poland flows directly into Polish territory, or if that is not sufficient, the pipeline can also operate in reverse to send more to Germany's eastern neighbor.
Since December 21, the pipeline has been operating in reverse, with gas flowing east back into Poland from the German border, according to data from management company Gascade seen by AFP.
This means that over the last days, Germany itself has not been receiving gas via Yamal.
Meanwhile, Russian gas continues to flow to Europe through other major pipelines such as Nord Stream I and TurkStream.
It is not unusual for the Yamal pipeline to operate in reverse for short periods, but this latest about-turn comes against a backdrop of political tension over fears that Russia may invade Ukraine.
In Germany, the government has said that in the event of any "escalation", it will put the brakes on another gas pipeline, Nord Stream 2, which is still awaiting the green light from the authorities.
Some European states, such as Poland and Ukraine, have accused Moscow and Russian energy company Gazprom of cutting gas supplies to Europe to exert political pressure over these tensions.
Russian President Vladimir Putin has said the change in gas flow through the Yamal pipeline is purely down to fluctuating orders and denied any political motive.
Gazprom, for its part, has called accusations that it is failing to deliver enough gas to Europe "absolutely groundless and unacceptable" and blamed Germany for dipping into its reserves to supply neighboring Poland.
Berlin on Monday denied any intervention on its part. "It is not the government that decides on gas flows, but the market, the traders," the Economy and Climate Ministry said.
According to George Zachmann, a specialist in energy issues for the Brussels-based Bruegel think tank, Gazprom may also be "favoring its own pipelines" over those it does not 100% control, such as the Yamal pipeline.
A spokeswoman for the German Economy and Climate Ministry told AFP that "security of supply is still guaranteed."
But Berlin, which has "relatively low" gas reserves with its tanks just 53 percent full, could soon have "difficulties", according to Christophe Bonnery, president of the Association of Energy Economists.
"If contracts are adhered to there will be no problems until at least March," said Zachmann. But "if Russia cannot or will not deliver gas for technical or other reasons, then supplies could fall short."
The wrangling comes amid an explosion in gas prices, which are up to seven times higher than at the beginning of the year.
The surge is thought to be partly down to a particularly cold winter and an increase in activity linked to the post-coronavirus economic recovery.
With 40% of gas consumed in Europe coming from Russia, Moscow is suspected of taking advantage of the tensions on the world market to reduce supply and drive up prices.
The International Energy Agency (IEA) in September called on Russia to be a "reliable supplier" and send more gas to Europe.