Configurational-bias Monte Carlo simulations in the grand-canonical ensemble are employed to compute adsorption isotherms of methane, ethane, propane, butane and binary mixtures of methane-ethane, methane-propane, ethane-propane, and methane-butane in the zeolite silicalite. Comparison of the simulation results with the limited experimental data available shows good agreement For ethane at room temperature,, a small inflection point in the isotherm was observed due to a surprising ordering of the ethane molecules in the zeolite. For the simulation of a methane-ethane mixture, at low pressure ethane is preferentially adsorbed, while at high pressures methane replaces ethane due to entropic effects.