Abstract Assessment of well integrity has become more important for CCS and CO 2 -EOR as it has become apparent that wells represent the most likely migration pathway for CO 2 to leave a CCS storage unit or a CO 2 -EOR reservoir. Although wells represent a migration pathway they are also the best vehicle for employing technology monitoring CO 2 injection and storage. This contradiction of being a potential migration path and key monitoring technology leads to a need to understand how monitoring wells may be similar or different in comparison to other types of wells with respect to migration risk. The maturation and completion US Department of Energy sponsored research projects presents an opportunity to assess the integrity of monitoring wells that have been exposed to injected CO 2 . This paper discusses an integrity assessment of two monitoring wells in an operating CO 2 -EOR flood in Mississippi, USA. It provides an early assessment of how monitoring equipment affects well integrity and isolation capacity. Each of the monitoring wells in this study were similarly constructed using both fiberglass and conventional steel casing. Each of the wells was instrumented with multiple monitoring technologies including, electrodes, pressure gauges, and temperature sensors on the outside of the casing. Control lines and cables were run from the surface on the outside of the long-string casing in each well to communicate with the monitoring equipment. A comprehensive logging, testing, and sampling program was developed to assess integrity in both wells. Ultrasonic well mapping was used to create radial maps of the location of cement, liquid, and gas behind the casing. Cement bond logging provided information on the casing-to-cement and cement-to-formation bonds for the long-string section. The logs showed that the monitoring equipment attached to the long-string casing is visible as continuous low acoustic impedance features and may represent a leakage risk. Cased-hole sidewall cores were collected and provided some validation of the log results and provide local information on the isolation capacity of the wells. The combination of information from the log data sets and cores was used to assess isolation capacity. The results of the study show that careful design and assessment of the materials used in monitoring well construction, the types of monitoring technology, and the location of monitoring technology within a well needs to be conducted with limiting migration potential and maximizing well integrity as objectives.