The adsorption of linear and flexible polyatomics on honeycomb, square, and triangular lattices is studied by combining theoretical modeling, Monte Carlo simulations, and experimental results. In the case of flexible k-mers, simulation data are compared with the corresponding ones from the well-known multisite Langmuir model (MSL) of Nitta et al. [J. Chem. Eng. Jpn. 1984, 17, 45], while in the case of rigid k-mers, computational results are correlated from the model for linear adsorbates (MLA) developed by Ramirez-Pastor et al. [Phys. Rev. B 1999, 59, 11027]. On the other hand, it is shown that it is possible to interpret all adsorption isotherms (for linear and flexible adsorbates) by using the recently reported fractional statistical theory of adsorption of polyatomics (FSTA) of Riccardo et al. [Phys. Rev. Lett. 2004, 93, 186101], with an adequate choice of the fundamental parameter of the model, g, being the measure of the statistical exclusion of adsorption minima. In addition, experimental adsorption isotherms for O-2 and C3H8 adsorbed in 5A and 13X zeolites, respectively, were analyzed in terms of FSTA. The more general character of FSTA with respect to the existing models and the satisfactory comparison with simulation and experimental results make the new theoretical model an attractive one for the description of adsorption of polyatomic particles with different sizes and shapes.