When establishing a farm of wind turbines it is of importance that an estimation of possible risks for the animal populations is performed on a proper basis. Until recently, little has been known about the behaviour of bats in the proximity of offshore wind farms. This report summarizes the experiences of a study aiming to analyze in what range bats passing or hunting near offshore wind turbines are exposed to collision risks. It also identifies the factors that might affect the risks of bat mortality caused by offshore wind energy. In the report conclusions are drawn from a total of more than 12 000 bat observations along Kalmarsund on the Swedish east coast and in Öresund between Sweden and Denmark. The results include information on activities of 10 different species of bats observed out at sea and 13 at coastal take-off sites. The report is a good guide on how to successfully mitigate potential risks for bats when locating offshore wind energy installations. It should be of value when planning Environmental Impact Assessments and monitoring programmes.