Multisite-occupancy adsorption is described by using a new formalism based on the occupation balance approximation (Romd, F.: Ramirez-Pastor, A. J.; Riccardo, J. L. J. Chem. Phys. 2001, 114, 10932). In this framework. the adsorption isotherm is characterized by a correction function 1, which relates to the conditional probability of finding the ith empty site to a lattice with i - I already vacant sites. A simple semiempirical adsorption isotherm is proposed by approximating e as a combination of the correction functions corresponding to exact I-D calculations and the Guggenheim-DiMarzio approximation, with adequate weights. Results are compared with corresponding ones from Monte Carlo simulations.