Energy dependence of strangeness production

We present a summary of strange particle yields measured by the experiment NA49 in central Pb+Pb collisions in the beam energy range 20-158 AGeV. The comparison with thermal hadron model results shows that above 30 AGeV, a strangeness undersaturation parameter $\gamma_S$ must be employed to describe the data. This suggests a change in the strangeness production mechanism at this energy. We find that the UrQMD transport model in all cases underpredicts the observed particle yields.