Abstract. The transverse mass spectra of high statistics, high purity samples of K 0 S , Λ, Ξ and Ω particles produced in Pb-Pb collisions at SPS energy have been studied in the framework of the blast-wave model. The dependence of the freezeout parameters on particle species and event centrality is discussed. Results at 40 A GeV/c are presented here for the first time.