Oil rallied to the highest level in more than four months as a fresh wave of US sanctions against Russia’s energy industry threatened to crimp supplies, sowing confusion among key importers in Asia.

Brent advanced toward $81 a barrel, after surging almost 4% in the previous session. West Texas Intermediate was near $78. The US imposed its most aggressive and ambitious sanctions yet on Russia’s oil industry on Friday, targeting large exporters, insurance companies, and more than 150 tankers.

The moves — less than two weeks before US President-elect Donald Trump takes office — throw a spotlight on India and China, with refiners potentially being forced to seek alternative supplies. India emerged as a vital buyer of Russian crude after Moscow’s 2022 invasion of Ukraine, and China is the world’s largest oil importer. Futures in Shanghai surged by the daily limit.

In China, independent refiners in Shandong held emergency meetings to try and work out if they could still take delivery of crude en route when the penalties were announced, traders said. In India, refinery officials said they were bracing for major disruption, which could last up to six months.

Crude has rallied in recent weeks, with gains spurred by colder weather, falling US stockpiles, and speculation that Trump officials may tighten curbs against flows from Iran in the coming months. The broad sanctions package from the outgoing Biden administration threatens to bring fresh disruption, potentially changing the market framework for OPEC+ as the alliance plans to start loosening output curbs later this year after a series of delays.

Closely watched metrics point to tighter conditions. Among them, Brent’s prompt spread — the difference between its two nearest contracts — was $1.21 a barrel in backwardation, a bullish pattern. That’s more than three times a month ago.

The jump in prices may also provide a challenge for central bankers, including the Federal Reserve, if it leads to stickier inflation. Investors have been scaling back expectations for the pace of interest-rate cuts from the Fed this year, with the US economy proving to be robust and price pressures lingering.

While it remains uncertain how the curbs will impact actual flows of crude for producers, shippers, traders and users, some early signs of disruption were apparent. Three tankers carrying more than 2 million barrels of Russian oil were floating in waters off eastern China after they were sanctioned.

Among banks, Citigroup Inc. said that up to 30% of Russia’s so-called shadow fleet of tankers could be affected, threatening as much as 800,000 barrels a day, although the effective loss may be less that half that. Goldman Sachs Group Inc. said it hadn’t changed its expectations for Russian supply as crude could be priced even more cheaply to incentivize buying.

Morgan Stanley raised its Brent forecasts modestly. The “new US sanctions on Russia’s oil industry went further than expected,” commodities strategist Martijn Rats said in a Jan. 13 report. “It will take some time to digest these measures, but this creates downside risk to oil supply, at least for a period.”

The wider OPEC+ alliance, which includes Russia, has been planning to revive production in stages from April after a series of deferrals, and its members have substantial spare capacity at their disposal. OPEC itself will issue its latest analysis on the state of the global market on Wednesday.

With price swings picking up, parts of the so-called paper market have been flashing warning signals. Oil options have regained a bullish hue, with a gauge of implied volatility rising as skews increased their bias toward call options as of Friday’s close.