The full-length paper introduces a new approach for modeling progressing-cavity-pump (PCP) performance. Slip flow is modeled as the result of rotor movement and differential pressure between cavities. The assumption was made that the slippage gap area depends on stator material. A strong relationship between slippage gap area and differential pressure is demonstrated. Internal stator deformation is identified as the main parameter necessary for predicting elastomer-stator-PCP performance. Although the proposed model is not able to fit data for all PCP models, its results agree with documented PCP-performance theory.