Experimental and numerical studies on oblique reflection are shown for weak shock waves in carbon dioxide. The reflection patterns are observed in density contour fringes by using a Mach‐Zehnder Interferometer, and classified into four types by combinations of fully and partly dispersed waves in incident, merged (or Mach) and reflected shocks. The regions and transitions lines of reflection types are shown in a Ms‐&thgr; (Mach number‐ramp angle) plane. The reflection systems are additionally classified into two types of quasi‐regular reflection and quasi‐Mach reflection for partly dispersed waves. The detachment criterion of two‐shock theory can give a good prediction for transition from quasi‐regular reflection to quasi‐Mach reflection. Numerical simulation is carried out for a fully dispersed wave by using the MacCormack‐FCT combined method, and found to be in a good agreement with the experimental observation. Furthermore, the numerical results indicate the types of quasi‐regular and quasi‐Mach reflection also for fully dispersed waves.