This is called settlement overhead, and is the reason you're incorrect. Every time you change one currency for another on any meaningful scale, it eats into your profit margin..
Tl;Dr - there's no such thing as "no foreign transaction fee!!!1!" in oil baron sized transactions.
Think a little bit wider than that. How do you pay your staff in the local area you work in? How do you pay taxes to the local government? How do you sell your oil to people who don't have, or don't want to, hold dollars. Are you really going to turn them down just because they hold GBP?
That's the whole point though, those people don't really exist. Basically everyone who does business internationally is, well, doing business internationally. You can either restrict your market to only people who hold your non-dollar currency, hold every currency in the world, or hold dollars. And keep in mind, everyone else holds dollars...
This is sometimes referred to as the network effect.
This is called settlement overhead, and is the reason you're incorrect. Every time you change one currency for another on any meaningful scale, it eats into your profit margin..
Tl;Dr - there's no such thing as "no foreign transaction fee!!!1!" in oil baron sized transactions.