This work deals with the ultrasound technology and their applications in the petroleum industry. The investigations in this study specialize in the treatment of water that is co-produced during oil production. This water contains various impurities and bacteria, which can cause corrosion, damage and plugging of the production conditioning- and water injection system. It also could lead to development of harmful and health hazardous gases. By injecting into the reservoir the bacteria can lead to the so called "souring" of the reservoir. Ultrasound can disable bacteria quickly and above all environmentally friendly. This work demonstrates the effectiveness of ultrasonic radiation against bacteria as well as the advantages and disadvantages of this treatment method for large-scaled use in comparison with currently used techniques in the petroleum industry such as biocide or UV-irradiation. With the results obtained in the laboratory, models are made for a scale-up in order to calculate costs for a large plant.