Just cam back from Africa. As Armen Fireman pointed out: West African countries (Congo and Niger in our case) were happy to take Euros.
Fuel Releases by Worldfuel were rejected twice and had to pay cash: in FCBB and DRZR (for the latter, the fuel release was issued on AirTotal, which had, however, pulled out of DRZR a long time ago...). Was glad to have plenty of extra cash with me to resolve those issues quickly!