Great explanations of the economics of a price cap on oil. I'm glad to see progress on this--it's a creative idea and IF it works it would be a big deal in helping to protect the global economy while maximizing the damage to the Russian war effort.
3 objections addressed below:

1. The West has no ability to stop Russian exports.
Harris goes through some of the ways that the West does have unilateral leverage. But if this turns out to be wrong then the cap won't work--but it also won't be needed for one of its objectives (protecting the global economy).

2. Russia will stop all of its exports in retaliation.
Maybe, I don't know. But I would note that if it does this that would go against one objective (protecting the global economy) but would outperform on another objective (punishing Russia).

3. There will be lots of leakage because of the powerful incentives for side deals, kickbacks and the like.
Surely this is true, but objecting to trying the plan based on this objection is a textbook case of letting the perfect be the enemy of the good.

Western countries need to be in this for the long haul. Will requiring figuring out how to deny Russia funds w/o unsustainable damage to themselves. A lot of obstacles to this working but it would be good enough that I'm glad they're trying hard to see if they can be overcome.