BACKGROUND. Shift work is related to fatigue and desynchronization with the external environment. This study investigates how 6-h shifts and 12-h shifts affects sleep and safety in workers onboard offshore supply vessels, and if any differences exist between the two working schedules. MATERIAL AND METHODS. A questionnaire study was carried out in the North Sea, Australia, Africa, South America, and the Far East, with 577 participants. The offshore fleet workers gave information on parameters related to sleep disturbances, causes of sleep disturbances, and safety. Regional differences in these parameters were also investigated. RESULTS. Workers on 6-hour shifts reported significantly more sleep problems than 12-hour shift workers did (p 〈 0.01). The 6-hour workers were more affected by noise (p 〈 0.01) and shift-work itself (p 〈 0.01). CONCLUSIONS. Those working 6-hour shifts suffer more from sleep disturbances than those on 12-hour shifts, but this is not reflected in the perception of safety within the individual. Noise and shift-work itself is more of a problem in the 12-hour workers. Differences in safety culture and work morale are likely to cause the differences between regions.