In this article we study the effects of adsorbed phase compression, lattice structure, and pore size distribution on the analysis of adsorption in microporous activated carbon. The lattice gas approach of Ono-Kondo is modified to account for the above effects. Data of nitrogen adsorption at 77 K onto a number of activated carbon samples are analyzed to investigate the pore filling pressure versus pore width, the packing effect, and the compression of the adsorbed phase. It is found that the PSDs obtained from this analysis are comparable to those obtained by the DFT method. The "discrete nature of the PSDs derived from the modified lattice gas theory is due to the inherent assumption of discrete layers of molecules. Nevertheless, it does provide interesting information on the evolution of micropores during the activation process.