  We study robust mechanisms to sell a common-value good. We assume that the
mechanism designer knows the prior distribution of the buyers' common value but
is unsure of the buyers' information structure about the common value. We use
linear programming duality to derive mechanisms that guarantee a good revenue
among all information structures and all equilibria. Our mechanism maximizes
the revenue guarantee when there is one buyer. As the number of buyers tends to
infinity, the revenue guarantee of our mechanism converges to the full surplus.
