  Let X be a cubic surface over a local number field k. Given an Azumaya
algebra on X, we describe the local evaluation map X(k) -> Q/Z in two cases,
showing a sharp dependence on the geometry of the reduction of X. We show that
a suitably generic cubic surface over a number field, whose reduction at some
prime is a cone, has no Brauer-Manin obstruction. This extends results of
Colliot-Th\'el\`ene, Kanevsky and Sansuc.
