We present three-dimensional numerical calculations of superbubbles evolving in a two-component interstellar medium composed of small diffuse clouds and a low-density intercloud medium. Cold H I clouds with internal densities n ˜ 10 cm-3 and radii Rcl = 3-5 pc were assumed to be embedded in a warm plane-stratified intercloud medium. The fraction of the total gas mass in clouds ranges between 0 and 0.5, whereas the cloud volume filling factor does not exceed 10%. The calculations determine the role played by dynamic disruption of clouds and by thermal evaporation from both the cold shell and the cloudy medium. It is found that mass loading from either disrupted or evaporated clouds dominates the mass input rate into the cavity, and the mass evaporated from the shell is important only at early times. The effects of differential galactic rotation, the gravitational field of the disk, and the location of the OB associations in the Galaxy are included also. The main properties of the giant remnants (energetics, morphology, total and X-ray luminosity, etc.) are estimated.