The sanctions threaten to take out “half” of those supplies, he said, given the measures prevent the two firms from selling their cargoes in dollars, the currency used almost exclusively for trading crude internationally.

For Lukoil in particular, the sanctions “will hurt significantly,” said one former executive at the company, who was granted anonymity to speak candidly about sensitive matters. The firm will likely have to sell its stakes in overseas projects from Egypt to Iraq, the person said, hitting up to 20 percent of its revenue.

But the majority of Chinese and Indian buyers, Russia’s two largest oil trading partners, are likely to continue importing from Moscow, said Homayoun Falakshahi, head of crude oil analysis at the Kpler commodities firm, given its cheaper prices and limited alternatives in the case of China.

After an initial period of hiatus, “most buyers would go back into buying,” he said, once they have found workarounds including purchasing cargoes via companies that obscure their Russian ownership.

“This will complicate exports and trade,” said Vladimir Milov, a former Russian deputy energy minister-turned-Putin critic. But “these companies … already have alternative work schemes in place, so there will be damage but it’ll be limited.”

On Thursday, Putin himself admitted the new sanctions were “serious,” while blasting the move as an “unfriendly act that does nothing to strengthen Russian-American relations.”