MOSCOW - A surprise decision by Russia to sell a fifth of its state-controlled oil company to, among others, a Swiss company has raised questions about the impact of Western sanctions and who is behind the deal.

The CEO of Rosneft said late Wednesday that it had agreed to sell a 19.5 percent stake to Swiss commodities giant Glencore and Qatar’s sovereign wealth fund.

The move was billed as part of the Russian government’s efforts to unload some state assets to help balance its budget amid a two-year recession caused by a drop in global oil prices and by Western sanctions against Russia.

The presence of Glencore in the deal, however, has raised eyebrows since the Russian oil industry is supposed to be off limits for Western investors because of European and American sanctions imposed on Russia. And the terms of the deal are not clear, with an unnamed bank taking a prominent role.

Here’s a look at the deal.

Why is it a surprise?

As part of Russia’s privatization drive, Rosneft was scheduled to sell a chunk of its shares by the end of the year. Rosneft is run by Igor Sechin, Putin’s long-standing ally, who is believed to wield almost unrivalled influence in the Russian energy sector and beyond. Earlier, Rosneft was reported to be inclined toward buying back its own shares instead of raising money through a sal...