This master thesis addresses the topics of organisational learning, lessons learned and challenges for their implementation for project based organisations. The purpose is to encourage lessons learned practices at AkerBP through the evaluation of Ivar Aasen field. This is done by doing qualitative analysis of information from respondents through surveys and interviews. The aim is to provide AkerBP with the best possible approaches for lessons learned to improve organisational learning. The findings and recommendations of this thesis will be guidelines for the case company for future projects. The surveys were conducted through two questionnaires and interviews were followed up after first online survey. The questions in questionnaires and interviews were focused on the challenges which had their impact on HSE (Health, Safety and Environment), Operational Costs, Working Environment, Resource Productivity and Collaboration on Site (One Team). Questions related to management response and support, measures taken for technical and organisational challenges and possibility of avoidance of challenges were also asked. Second survey was conducted after interviews which was mainly focused on existing lessons learned practices and their implementation in the organisation. The interviews were conducted face to face and audio recorded. The findings are based on the information from 17 respondents. The literature review covers all basic concepts and challenges for organisational learning and competitive advantage through capturing, storing and transferring lessons learned effectively. Types of learning and management of lessons learned have also been discussed. Many possible approaches have been described based on different theories and categories which are helpful in selecting appropriate approach for organisational learning. It also focuses on the limitations and impediments to lessons learned practices. The findings suggest that people are willing to share and contribute in learning processes but there have been several challenges for them. The management also encourages learning on all levels, whether it is with internal or external resources or even informal discussions among employees. But the structure and processes appears to be a bit weak for learning and organisational culture of the case company. The challenges mentioned by respondents include excessive workload, reduced resources, lack of guidance, multiple systems interfaces and inefficient transfer of lessons learned across all levels. This master thesis is important for the case company as it identifies and highlights challenging factors in their existing processes. This thesis will contribute to improve their lessons learned practices and to achieve organisational learning to the highest level. It gives them a third party’s opinion as the recommendation for improvements will give them an initiative for future projects. Moreover, this thesis will fill the gap in research work especially the literature related to lessons learned practices during operation phase. It will be a valuable addition as a guide- line for similar projects.