A lattice-Boltzmann boundary rule has been developed to recover the slip boundary condition at a liquid-gas interface. This rule enables one to use a single-component lattice-Boltzmann model to simulate bubbly flows where bubbles are nearly spherical and coalescence is prohibited. Numerical tests showed this method to be robust and accurate in simulating both steady and unsteady flows around spherical bubbles in the Reynolds number range 0<Re<30.