  If $M$ is a compact or convex-cocompact negatively curved manifold, we
associate to any Gibbs measure on $\tm$ a quasi-invariant transverse measure
for the horospherical foliation, and prove that this measure is uniquely
determined by its Radon-Nikodym cocycle. (This extends the Bowen-Marcus unique
ergodicity result for this foliation.) We shall also prove equidistribution
properties for the leaves of the foliation w.r.t. these Gibbs measures. We use
these results in the study of invaiant meausres for horospherical foliations on
regular covers of $M$.
