Russia has been pushing for years to build a new pipeline to China to deliver billions of dollars' worth of natural gas to its close ally.
But progress has been slow amid hesitation in Beijing.
As Russian President Vladimir Putin arrives for talks with his counterpart Xi Jinping, here is what AFP knows about the proposed pipeline:
The 2,600-kilometre (1,600-mile) route would run from the Yamal peninsula in northern Siberia through Mongolia into China.
It would carry around 50 billion cubic metres of gas a year, equivalent to around 12 percent of China's estimated total gas consumption in 2025.
Crucially for Russia, the gas would be supplied from fields that previously served Europe, where exports of pipeline gas have plunged since Moscow launched its invasion of Ukraine in 2022.
That differs from the existing Power of Siberia pipeline, launched in 2019, which has the capacity to move around 38 billion cubic metres of gas annually from eastern Siberia to northeastern China.
"For Russia, it is a strategic lifeline after losing most of its European gas market," said Alexander Korolev, a political scientist at UNSW Sydney in Australia.
"For China, the pipeline is about energy security and leverage, and less about dependence. It diversifies supply away from maritime chokepoints," he said.
First proposed by Putin in 2006 alongside what became the first Power of Siberia pipeline, Beijing has said little about a second pipeline, and construction has not started.
Russia's state-owned Gazprom said last year that it had signed a legally binding 30-year supply agreement with the China National Petroleum Corporation (CNPC) that would underpin the pipeline.
But details were scant, including on the critical issue of price.
In a statement at the time, China's foreign ministry said only that Xi and Putin had signed "over 20 bilateral cooperation documents" in fields including energy, aerospace, artificial intelligence and agriculture, without mentioning the Power of Siberia 2.
China's attitude to the project for years was "if it happens, great, if it doesn't, we'll manage", said Alexei Gromov, head of the Russia-based Institute for Energy and Finance.
That may now have changed, as Russia hopes to seize on energy volatility triggered by the war in the Middle East and the closure of the Strait of Hormuz to kick-start the project.
"The current crisis could boost the chances of the Power of Siberia 2 pipeline being built," said Natasha Kuhrt, lecturer in international peace and security at King's College London.
"The first Power of Siberia pipeline took about 20 years or more to come into being, and the Chinese drive a hard bargain on price. On this second pipeline the story will be no different, the cards will all be in China's hands," she said.
Ahead of Putin's trip, Kremlin foreign policy aide Yuri Ushakov told reporters there would be "very detailed" discussions on the pipeline with Xi.
Analysts were divided as to whether a deal could be on the cards during this visit.
Gromov said he saw "quite high" chances of a full commercial deal being struck, while Korolev was more hesitant, expecting only "affirmation of political support, not final agreements".
Analysts attribute part of China's hesitance to Beijing's desire to balance energy imports from different suppliers and not become too reliant on any one source.
But since the West sanctioned Russia over its Ukraine invasion and cut its imports of Russian energy, China has lapped up discount oil from a key ally.
In terms of natural gas, China imported $2.3 billion from Russia during the first three months of this year, up three-fold from the same period in 2022, according to Chinese customs data.
Russian energy sales are the "most stable" part of a political, military and economic relationship that has blossomed between the two countries in recent years, Korolev said.
If completed, the Power of Siberia 2 "would deepen that interdependence" while also signalling that Russia "is not isolated and can still execute major infrastructure projects", he added.
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