Reservoir geo-modeling is a fundamental step of the multi-phased geo-energy maturation journey. It allows the description and quantification of the subsurface static and dynamic parameters, which will largely determine the success or failure of exploration, development and management of georesources. The geo-modeling exercise, based on careful data quality check and use of a-priori knowledge, is typically performed at the early stage of a geo-energy project and it is used both to test ideas on development strategy and quantify the economic aspects. From the quality and correctness of a geo-model therefore will depend important business decisions that will have a long-term impact on the overall geo-energy development journey. Inaccurate or wrong understanding of the subsurface at the early stage of a project will have a persistent negative impact on the destiny of the entire project, which very seldom will be improved by high-quality execution practices. In order to reduce the risks of failure of any geo-energy project, subsurface uncertainty identification, quantification and management will need to be considered. Fit-for-purpose models, able to represent different possible subsurface configurations and respond to a variety of project objectives and business questions, will need to be implemented. A reliable deterministic representation and quantification of the subsurface parameters can be thus obtained by a set of geo-models (subsurface realisations) aimed at capturing the full possible range of both geological and fluid behaviour characteristics. These will be a solid basis for planning the development strategy, defining economic forecasting and moving in to project execution while providing a realistic description of the associated risks.