A method for managing the asset portfolio of an oil E&P company is proposed based on marketing planning techniques proven within the commercial sector. A multi-tiered approach is adopted to allow consideration of assets, both producing and prospective, within a regional, national or basinal context. The use of life-cycle concepts, gap analysis and directional policy matrices to evaluate and rank assets is illustrated through reference to a typical diversified North Sea portfolio. The implementation of these techniques within a company environment is also discussed. As well as allowing properties at different stages of maturity to be compared, appropriate strategies on how to manage the assets at each stage of development can be deduced from the categorisation introduced by the policy matrices. The method presented also allows the forecasting of potential shortfalls in production and facilitates strategic planning decisions to change the nature and size of the portfolio. The method is considered to be rigorous and rational and constitutes an improved, auditable technique for E&P portfolio management.