Even after waterflooding is applied, the average recovery factor from conventional oil fields is between 25-45%, which means that a major part of the oil still remains in the reservoir. In case of field in Austria, waterflooding is already applied for several decades. A large portion of the produced fluids is reservoir water (i.e. 96% water cut) implying that the remaining oil is largely trapped. Therefore, new methods and techniques need to be applied. Enhanced oil recovery (EOR), as the name indicates, summarizes techniques that deal with the increase of hydrocarbon recovery from fields depleted by conventional means. One family of techniques is chemical flooding, for which the targeted field is suitable. Alkaline flooding is one promising method, creating in-situ surfactants thus lower the interfacial tension between oil and water. Furthermore, alkaline flooding preconditions the reservoir for a subsequent surfactant polymer (SP) flood. The present thesis investigates the behavior of the interfacial tension (IFT) between various oils and injection water of different chemical compositions. The oil samples crude 8 and crude 16 are characterized by a relatively high total acid number (TAN), which makes them a target for alkaline flooding. As alkalic EOR agent, sodium carbonate (Na2CO3) has been added in different concentrations to distilled water and synthetic brine mimicking the reservoir water. For first orientation classical phase behavior experiments were conducted to investigate the degree of emulsion formation. To measure IFT pendant drop and spinning drop methods were applied. During the study it turned out that spinning drop can be applied throughout the whole range of investigated IFT, while pendant drop failed below a value of 1 mN/m. The bulk of experiments were performed at ambient conditions, and temperature dependencies were determined for selected interesting cases. Experiments conducted with distilled water solutions showed a distinct reduction of IFT and pronounced emulsion formation. However, different oil samples showed different trends without a clear link to the TAN. The synthetic brine solutions on the other hand showed neither a distinct reduction nor visible emulsion formation, not in spinning drop nor in the phase behavior experiments. At last, temperature dependencies were investigated which showed that IFT readings are sensitive to it. The individual fluid combinations show distinct behavior, but without an obvious trend with respect to alkali concentration and TAN. Further statements require additional experiments.