Several experiments have evidenced the occurrence of saturation overshoots for flows in homogeneous porous media. Such phenomena are ruled out by standard mathematical models, which are based on equilibrium assumptions. In this presentation we discuss nonequilibrium models, in particular including dynamic effects in the capillary pressure. This leads to extensions of the classical Buckley-Leverett (BL) equation, a commonly accepted model for two-phase flow in porous media. For this extended equation we investigate the existence of traveling wave solutions. Based on this we explain the occurrence of saturation overshoots, and discuss the profiles obtained for one phase or two phase flow models.