  We derive a revenue-maximizing scheme that charges customers who are
homogeneous with respect to their waiting cost parameter for a random fee in
order to become premium customers. This scheme incentivizes all customers to
purchase priority, each at his/her drawn price. We also design a
revenue-maximizing scheme for the case where customers are heterogeneous with
respect to their waiting cost parameter. Now lower cost parameter customers are
encouraged to join the premium class at a low price: Given that, those with
high cost parameter would be willing to pay even more for this privilege.
