How do export duties work?

[Buzz cook]

My sense of them is that they are a tax/fee levied on goods before they leave the country and paid by the entity doing the exporting. Or are they paid by the entity in the other country that is buying the goods?

Trump has not put a tariff on the import of Canadian oil. If our Canadian friends want a little tit for tat, then wouldn't an export duty on oil hit that tit right in his orange face?

Of course if I'm wrong, well never mind.