One and two-component colloidal particles, sulfate-treated polystyrene (S-PS), aldehyde-sulfate (AS-PS), and carboxylate-treated polystyrene particles (C-PS), were assembled at air/water interfaces by injecting particle dispersions. Surface pressure-area (π-A) isotherms were measured using the Langmuir-Blodgett technique. The isotherms for S-PS particles are reversible and independent of barrier speeds during the compression/relaxation cycles. The normalized isotherms of S-PS/AS-PS and S-PS/C-PS particle mixtures lie between those of single species. In addition, the self-assembled structures of particles were transferred onto mica substrates and characterized using a laser scanning confocal microscope. The morphology of the two-component layer has the characteristics of both single component layers with no significant phase separation. Finally, we have explored the potential applicability of a purely additive group contribution analysis to surface pressure-area isotherms.