A series of carbon molecular sieves (CMSs) has been prepared, either as powders or monoliths, from petroleum pitch using potassium hydroxide as the activating agent. The CMS monoliths are prepared without the use of a binder based on the self-sintering ability of the mesophase pitch. Characterization results show that these CMSs combine a large apparent surface area (up to ca. 3100 m2 g−1) together with a well-developed narrow microporosity (Vn up to ca. 1.4 cm3 g−1). The materials exhibit high adsorption capacities for CO2 at 1 bar and 273 K (up to ca. 380 mg CO2 g sorbent−1). To our knowledge, this is the best result obtained for CO2 adsorption using carbon-based materials. Furthermore, although the CO2 adsorption capacity for activated carbons has usually been considered lower than that of zeolites, the reported values exceed the total amount adsorbed on traditional 13X and 5A zeolites (ca. 230 mg and 180 mg CO2 g sorbent−1, respectively), under identical experimental conditions. Additionally, the narrow pore openings found in the CMS samples (ca. 0.4 nm) allows for the selective adsorption of CO2 from molecules of similar dimensions (e.g., CH4 and N2).