The West is rolling out increasingly tough sanctions on Russia but it is going out of its way to preserve the country’s biggest source of revenue: energy exports.

In the latest example, the European Union said late Saturday that it had agreed with the U.S., the U.K. and Canada to eject some of Russia’s banks from the global financial system’s payments infrastructure, Swift. The move, if applied to all banks, would be powerful, essentially blocking money transfers in and out of the country. By cutting only some, Western countries are allowing payments, including for energy, to continue through non-sanctioned banks.