"Europe clearly needs to reduce its dependence on Russia with respect to energy, but we need to be careful when we think about a complete European ban on, say, oil imports," Yellen said.
[...]
"That would clearly raise global oil prices, it would have a damaging impact on Europe and on other parts of the world, and, counterintuitively, it could actually have very little negative impact on Russia, because although Russia might export less [to the EU], the price it gets for its exports[, of say, oil] would go up," Yellen said.

"Proceeds from sales of oil and gas are an importantsource of income for Russia. It would be very useful to try to devise a way to reduce Russia's proceeds from those sales income," Yellen said.

"That really is the proper objective of a ban [on European purchase of, say, Russian oil]. But if we could figure out a way to do that without harming the entire globe through higher energy prices[, or, say, USD-denominated penalties added to purchase of Russian oil by "third-countries"], that would be ideal. And that's a matter that we're all trying to think through together," she continued.