There have been several major offshore accidents in different offshore regions since 2005. In Norway there have been several very serious near-misses during the last ten years, several of which involving serious hydrocarbon leaks with catastrophic fire and explosion potential. All these severe occurrences demonstrate the importance of learning from major accident precursors in order to appraise the risk potential involved in critical offshore operations. This paper is based on analysis of about 175 hydrocarbon leaks in the period 2001-2010. Regulatory requirements in Norway are aimed at preventing as far as possible such occurrences during night time, but the analysis shows that this has been far from successful. The industry has for many years claimed that the maintenance personnel are the main group of employees involved in causing these leaks. This study has shown that leaks during the execution of maintenance and modification are less than half of the leaks, and that failures during the preparation for carrying out maintenance tasks are more frequent. Such preparations have often been conducted during night shift. The analysis gives a strong incentive to change this practice. (C) 2012 Elsevier Ltd. All rights reserved.