Nucleation and growth of bubbles in porous media are important problems encountered in processes such as pressure depletion and boiling. Experiments and numerical simulations are studied in micromodel geometries to understand their basic aspects. Experiments of bubble growth by pressure depletion are carried out in 2-D etched-glass micromodels and in Hele-Shaw cells. Nucleation of bubbles and subsequent growth of gas clusters are visualized. Contrary to the bulk or Hele-Shaw cells, gas clusters in the micromodel have irregular and ramified shapes and share many of the features of an external invasion process (such as percolation during drainage). A pore network numerical model developed simulates the growth of multiple gas clusters under various conditions. It is based on the solution of the convection-diffusion equation and accounts for capillary and viscous forces, which play an important role in determining growth patterns. Numerical simulation agrees well with the experimental results.