I&#x27;ve been left wondering how the Mondo&#x2F;Mastercard rate actually works: yes they pick some rate based on X, Y and Z, but how does this interact with the market described in the post?<p>I suspect not very much at all, at least for major currencies, as Mastercard has people buying $ for £ in the UK, and £ for $ in the US, so they only need to go onto the market for the imbalance, allowing an &quot;incredibly good&quot; rate, when they&#x27;re not  exchanging much on the open market at all...