For supercritical fluids there is a wedge-shaped region called Widom region, where several physico-chemical quantities (e.g., compressibility, heat capacities, density, thermal expansivity, speed of sound) show anomalous behaviour. In this paper several Widom lines of supercritical CO 2 have been computed with the Wagner-Span reference equation of state. The locations of the Widom lines are compared with the P-T range of the Snøhvit, Sleipner, Nagaoka and Ketzin reservoirs, which are recently studied for their fitness for CO 2 sequestration, and two natural CO 2 storage analogues, Montmiral in France and Mihályi-Répcelak in Hungary. The potential consequences of leaking CO 2 crossing any of the Widom lines are discussed.