Cotangent cohomology of rational surface singularities

In this paper we show that the number of generators of the cotangent cohomo logy groups T-Y(n), n greater than or equal to 2, is the same for all ratio nal surface singularities Y of fixed multiplicity. For a large class of rat ional surface singularities, including quotient singularities, this number is also the dimension. For them we obtain an explicit formula for the Poinc are series P-Y(t) = Sigma dim T-Y(n) . t(n). In the special case of the con e over the rational normal curve we give the multigraded Poincare series.