The binding mean spherical approximation (BiMSA) is used to describe osmotic coefficients for aqueous solutions of salts containing alkylammonium cations or bulky anions. A total of 35 salt solutions is accurately described at 25 degrees C over the whole concentration range, up to very high concentrations such as 20 mol.kg(-1) for methylammonium chloride or 24 mol.kg(-1) for ammonium thiocyanate. The ion diameters, the permittivity of solution, and the association constant are adjustable parameters within the BiMSA model. New diameter values are assigned to alkylammonium cations and bulky anions such as tetrafluoroborate, alkanesulfonates, methylsulfate, trifluoroacetate, or trifluoromethanesulfonate anions. Alkylammonium sizes are in reasonable agreement with literature values. Besides, association constants values obtained within the BiMSA model compare well with literature values when available.