After months of planning and negotiations, the biggest tranche of sanctions on Russian oil to date take effect on Monday. How big their impact will be remains uncertain.

The Group of Seven clinched a last-minute deal to cap the price of Russian crude at $60 per barrel. Anyone wanting to access key services that the bloc provides — especially insurance — will have to pay that price or less. The same goes for European tankers, especially the giant Greek fleet.

But there are still enormous unanswered questions that will shape the impact of the measures on the oil market, including the depth of non-European insurance markets, the appetite of some tanker owners to participate in trade with Russia, and exactly how effective enforcement of the cap can be.