The area-dependent pressure change, pi-A curve, was measured for the monolayer of an amphiphilic fatty acid containing phenyl and diacetylene groups. It was found that the pi-A curve showed such notable characteristics as "overshoot hump", "zero surface pressure", and "flat plateau", depending on various experimental parameters, including the subphase composition, temperature, and compression rate. The essential aspect of the experimental trend in the pi-A curves was successfully explained with the aid of a computer simulation, which included the effect of autocatalytic and cooperative aggregation of the fatty acids at the air-water interface under nonequilibrium conditions.