Abstract Hazards have been referenced by the functional element to which they are associated: Reservoir, Caprock, Faults, CO 2 , Overburden, Underburden, and Wells.They have been classified according to the detectable undesired event that they could potentially lead to, in the context of CO 2 injection in the subsurface. When a hazard can lead to several events, it has been repeated in the relevant sections of the table. A high level review of the potential consequences of each undesired event is provided in the column “Consequences”. It is understood that the consequences of the same event could be different, depending on the hazard which is causing this event. Nonetheless, as this is a preliminary exercise this fact has not been formally represented in the table.Finally, a high level screening of the potential prevention measures that could be put in place at different phases of the project (appraisal, construction, injection/monitoring) as well as mitigation measures are provided in the last column of the table.This list is not meant to be exhaustive but its objective is rather to highlight the most important technical risks associated to the project and plan accordingly for the next phases (in particular the appraisal). As mentioned before, due to the early stage of the project, a quantitative assessment of the risks has not been performed as part of this task. However, a preliminary analysis of the criticity of the risks associated with the identified hazards was conducted with the objective to highlight what were felt as the major concerns concerning the two candidate sites at this stage of the project.Again, the data currently available not allowing us to discriminate meaningfully between the two zones, this has been kept as a common exercise. At this early stage of the project, only a preliminary risk assessment is possible, with the following consequences: no risk scenario has been explicitly described, but only individual hazards (which will form the “building pieces” of risk scenarios); no quantitative evaluation of severity and likelihood has been made; each of the two candidate zones has specific risk factors. However, given the current level of understanding, it has been decided that a meaningful discrimination between the two zones was not yet possible and therefore, the exercise has been kept as common for both zone 1 and zone 5. Hazards and undesired events must be defined as deviations from a “base case” scenario. The characteristics of this base case are:the injected CO 2 stays within the planned reservoir formations; CO 2 never reaches the bounding faults, which are nevertheless assumed as sealing;no unplanned shut down of injectors during the injection phase. all existing wells are sealing; injection rates and quantities as per plan and used in the Eclipse simulations. It is important to stress that risk analysis is a continuous and iterative process, and that more accurate information from appraisal, verification and monitoring can improve the knowledge of a storage site, and can therefore adjust the severity and likelihood defined for each risk, and can finally lead to an updated mitigation and prevention plan (including monitoring). The workflow for a complete risk analysis and monitoring plan is as follows:define severity (i.e. impact) levels for each stake (health, financial, safety, and environment), according to the risk matrix of the organization; define likelihood (i.e. probability) levels; identify all project risks associated with performance reduction. The key performance indicators are injectivity, capacity and containment Evaluate their likelihood and severity; place them in the Risk Matrix to identify scenario (hazard – event – consequence) with the highest criticity; prepare mitigation plans to reduce likelihood and prevention plans to reduce severity to such levels that all the residual risks are within the acceptable levels for the organization (including local/ international regulations etc.)