This report discusses localisation of underwater sources using passive acoustic arrays from FOI's sensor system PASS. Localisation performance depends on how well calibrated the antenna is, but also on the source level and spectrum as well as local sound propagation characteristics. By analyzing several passages of civilian vessels, it is shown that one can achieve satisfactory localization at ranges up to 4000 meters. This requires that the arrays are accurately calibrated. The report introduces several calibration methods and compares their relative merits and drawbacks. It shows that PASS antennas can be sufficiently curved so that site-specific calibration is required, and that calibration using motor boat noise from own boat or passing vessels whose positions are obtained from AIS data can offer the same localization performance as can be obtained when using calibration based on short sonar pulses transmitted from several different locations near the antennas. TDOA-based methods can handle any array geometries, but DOA-based methods can perform better in low SNR.