The aim of this thesis is to evaluate different repowering alternatives from the viewpoint of increasing power production from existing offshore wind farms (OWF), as some of the first commissioned OWFs are approaching the end of their expected lifetime. The thesis presents a literature review of components and financial aspects that are of importance for repowering of OWFs. In the literature review, risks and uncertainties regarding repowering are also lifted and analysed. The thesis contains a case study on Horns Rev 1 OWF, where three different repowering scenarios are evaluated by technical and financial performance, aiming to compare the cost of repowering alternatives. The design of the case study is based around previous studies of offshore repowering having focused mainly on achieving the lowest possible levelized cost of energy (LCoE) and highest possible capacity factor, often resulting in suggested repowering utilizing smaller wind turbines than the existing ones. In order to evaluate the financial viability of repowering alternatives, the software RETScreen Expert was used to estimate the annual energy production (AEP) after losses and calculate the net present value (NPV) and LCoE for lifetime extension and full repowering utilizing different capacity wind turbines. Input values from the literature as well as real wind resource measurements from the site was utilized to achieve as accurate results as possible. The result of the case study shows that repowering of OWFs have the possibility of providing a very strong business case with all scenarios resulting in a positive NPV as well as lower LCoE than the benchmarked electricity production price. Although the initial investment cost of the different repowering alternatives presented in this thesis still are uncertain to some extent, due to the lack of reliable costs for repowering alternatives, this thesis provides a base for further research regarding the repowering of OWFs.