The post treatment in the BOF process is a very important process step to achieve low phosphorus contents and to reach the target temperature before tapping. Usually the post treatment methods are divided into two categories, the reblow and rerinsing of the melt. There is also the possibilty to add lime, ferrosilicon and BOF-Slag. This thesis is about the dephosphorization effect of the various post treatment methods, which are currently used at voestalpine Stahl GmbH in Linz. Several investigations were carried out in which steel and slag samples were taken after the main blowing period and after the post treatment. The different strategies of the BOF-leaders were investigated and checked for their plausiblity. In addition some of the already published dephosphorization models are explained and a comparison between the plant data and the predicted data of the models was done. A determination whether the models are suitable or not to predict the right phosphorus content was pointed out. The basic factors of influence were detected and discussed in comparison with the plant data, the thermodynamic calculations and the published data of the literature. Finally, the dephosphorization effect of the different post treatment methods were determined by evaluation of the plant data. A decision-model was developed to help the BOF-leaders to pick the right method depending on the limiting factors.