Equilibrium molecular dynamics simulations have been used to investigate the fluid adsorption phenomena and calculate the surface tension in porous media at different temperatures, densities and pore widths. The facts that most of the fluid particles are adsorbed adherent to the pore walls and the surface forms near the walls have been found, and that the surface is not stable which means there exists an oscillation phenomenon in pores have been also found. The surface tension in pores is much bigger than that in macrovolume systems like normal liquid-liquid and liquid-vapor interfaces, and it will increase with the increase of density and pore width, but will decrease with the increase of temperature. (C) 2002 Elsevier Science B.V. All rights reserved.