Using a four-country, two-tier macroeconomic model, it is shown that the pseudo-exchange rate union with the large partner has no effect on the real exchange rates of the small countries but affect their price levels, whereas a full monetary union requires in principle a transfer whose allocation between the two small countries by their common central bank may have real effects. This transfer is precisely provided by the large country, as guarantor of the fixed exchange rate arrangement. When both small countries are in surplus, there is a reverse transfer to the large country, with no monetary consequences. In line with the findings of the model, evidence is provided on monetary allocations in UMOA and on the real exchange rates of its major members, as compared to other African countries.