The reason for this Master Thesis was that RAG Rohoel-Aufsuchungs AG experienced an unsatisfying success rate in cement plug jobs in their wells in Austria in the past few years. So far, no reason could be identified why some plug jobs went well and others didn’t. The goal was to analyze previous plug jobs and identify possible error sources. The thesis gives a brief introduction on cement plugs, what they are used for and drilling problems that could be solved with such operation. Further on a cement plug operation is described from the planning, the cementation program and the activities on the rigs site. The main part of this work is the case study about the cement plug jobs from the last 6 years and a preparation of statistical data. Accordingly the critical parameters for such a job were identified and discussed in detail. The parameters are separated in two groups: unchangeable parameters (formation, inclination…) and changeable parameters (plug length, pump speeds…). To analyze the parameters in detail the available real time data from the rig site was processed. Together with cementing business unit of Schlumberger (SLB) simulations with their software Plug Advisor were performed to find possible error sources. The results of these simulations were discussed in this work. Further on this thesis gives an insight in the testing procedures and testing devises used in the cementing laboratory of Schlumberger. In addition to the general case study, a detailed analysis of the last 5 cement plug jobs of RAG was performed. A discussion of all critical parameters and possible causes for not satisfying results is part of this thesis. At the end a recommendation for an improvement of the plug success rate was discussed including alternative methods that are used in the industry.