  We show that a free surface in $P^3$ is characterized by the maximality of
the degree of its singular subscheme, in the presence of an additional tameness
condition. This is similar to the characterization of free plane curves by the
maximality of their global Tjurina number given by A. A. du Plessis and C.T.C.
Wall. Simple characterizations of the nearly free tame surfaces are also given.
