Abstract The existing data for wells in the Weyburn-Midale Field were used in conjunction with publicly available data to create an updated well integrity risk assessment as an aid in establishing CO 2 containment risk and developing a guide to selection of monitoring technologies for risk management. The assessment built upon an existing assessment to rank 1424 wells on 13 categories used as a proxy for likelihood of CO 2 migration and four categories used as a proxy for severity of impact of migration. The results of the assessment were used to show that both the risk posed by individual wells and risk posed by categories may be significant with respect to CO 2 migration. The location of the top of cement, quality of the casing, and type of well categories were ranked high throughout the distribution of wells with respect to likelihood of migration. The assessment of casing integrity and setting of casing through the Midale Evaporite was a differentiating factor between higher-likelihood and lower-likelihood well scores. The aquifer protection category used in assessing the severity of impact ranked high across the distribution of wells. The proximity to a water source category was a differentiating factor between higher-severity and lower-severity rankings. The wells scores and ranking categories were used to assess the value of specific monitoring tools for managing containment risks. The outcome of the study showed that both high risk wells and high-risk categories can be identified and that a monitoring program should be adopted to address both through point and area monitoring.