This study was designed to understand the possible impact of carbon dioxide on different reservoir rocks in south-central Mississippi. Eight samples, including six from the Heidelberg field (Mississippi), were exposed to carbon dioxide under simulated subsurface conditions of elevated temperature and pressure and then analyzed using thin section petrography, scanning electron microscopy, X-ray diffraction, and focused ion beam-SEM. Three of the eight samples showed dissolution in calcite and corrosion in smectite. SEM and EDS analysis of treated sample 5 (Se-5/shaly-sandtsone) and sample 8 (S-8/dolomitic-limestone) revealed newly precipitated lath- and fibrous-like crystals composed of sulfur (S), oxygen (O), and calcium (Ca), thus interpreted as gypsum. Three-dimensional analysis using FIB of dolomitic limestone samples (Smackover Formation) revealed that gypsum crystals fill fracture porosity. This study significantly contributes to the understanding of carbon dioxide impact on reservoir rock and promotes better management of natural gas resources.