This study addresses the problem of specification of physical models for quenched-fluorescence-based oxygen sensors by analysing their complex frequency response (both intensity and phase signals) at different working frequencies and oxygen concentrations. Two common physical models of active medium, the single-exponential model with non-linear oxygen solubility and the double-exponential model were considered, with the example of heterogeneous PtOEPK-PS-based oxygen sensor. It was found that within the limits of experimental errors, the non-linear oxygen solubility models describe more adequately experimental data for the sensor. Model parameters were defined and analysis of the sensors system performance at different working frequencies and oxygen ranges was made.