Different kinds of initial conditions for the gas-liquid process on a solid catalyst are discussed in the paper. The advantages of process with preliminary saturation of liquid with gas are considered. For the liquid batch reactor it is theoretically shown that preliminary saturation of the initial solution with gas prior to reaction profits more in comparison with "usual" mode. The experiments on hydrogenation of ethyl ether of p-nitrobenzoic acid to anesthesyne on suspended 5% Pd/C catalyst in a batch reactor were carried out for verification of the main results from the proposed model (P-H2 = 40 bar, T = 20-120 degreesC). As an example of a reactor, where the preliminary saturation effect can be used, the trickle-bed reactor operating without pumping was considered. Mathematical simulation of such type reactor is presented.