We have developed an extension of the Drude model for oscillators to determine capacitance in organic polymers. The extension covers the effect of time delay caused by dispersion in the carrier transport. This was done using a complex mobility parameter. Negative capacitance effect could be observed in simulation at low frequencies provided that model parameters are appropriately chosen. In matching the simulation results to a set of data reported [Phys. Rev. B. 63 (2001) 125328] we have computed very reasonable values of the transport parameters in regimes where either positive capacitance or negative capacitance is dominant. Negative capacitance effect was attributed to charge trapping in a dispersive media when the carrier mobility had a negative imaginary component. Qualitative agreement was achieved to first order between simulation and observation provided that a mild frequency dependence exists in the carrier mobility. We believe our model is a better approach to extract transport parameters from capacitance-frequency curves when detailed conduction processes could not be easily identified such as in an environment of disordered complex molecules. (C) 2003 Elsevier Science Ltd. All rights reserved.