  In the present paper we determine the Thurston-Bennequin invariant of graph
divide links, which include all closed positive braids, all divide links and
certain negative twist knots. As a corollary of this and a result of P. Lisca
and A.I. Stipsicz, we prove that the 3-manifold obtained from the 3-sphere by
Dehn surgery along a non-trivial graph divide knot K with coefficient r carries
positive, tight contact structures for every r except the Thurston-Bennequin
invariant of K.
