From experimental surface tension data for water solutions of dodecyl-beta-maltoside, C12M, and dodecyl-penta-(ethylene oxide), C12EO5, in the range below the CMC, the corresponding head group surface pressure functions vs. packing density were derived. These functions were compared with theoretical expressions based on some different models of the mixed head group/water film. Tentatively, we concluded that the two-dimensional hard fluid approach provides a convenient starting-point in order to account for the observed surface pressures of both the maltoside and EO head groups.