Plasma surface modification of polyimide (PI) films has been used to modify the material's wetting and adhesion properties but has also been found to impact high-field electrical properties. Previous work by Meddeb et al. (Chem Phys Lett 649:111-114, 2016. https//doi.org/10.1016/j.cplett.2016.02.037) demonstrates a significant reduction in high-field leakage current at high temperatures because of O-2 plasma treatment of PI. In this study, we investigate field-dependent current density [J(E)] data measured in our previous study by Meddeb et al. (2016) to identify the surface and bulk mechanisms responsible for high-field conduction behavior of O-2 plasma-modified PI films. Specifically, we analyze the J(E) data using three conduction theories: Poole-Frenkel, Schottky, and Hopping. Poole-Frenkel and Schottky analyses are performed by the implementation of linear regression. Hopping analysis was performed using a rigorous statistical technique that incorporates nonlinear regression as well as a bootstrap statistical analysis of fit parameters. Analysis of J(E) data over the temperature range 25-175 degrees C indicates that 13-micron-thick untreated PI films are dominated by a hopping process at lower temperatures; however, transition to Schottky-dominated conduction occurs as temperature is increased. Films treated with O-2 plasma show similar characteristics to the untreated set: Hopping dominated conduction at low temperatures with gradual transition to Schottky. However, the transition to Schottky conduction occurs at a higher temperature in plasma-treated films in comparison with the untreated control set. These results are verified by (1) extracting dielectric permittivity from Schottky plots as a function of temperature and (2) a statistical interpretation of confidence intervals calculated for hopping fit parameters used in low-temperature nonlinear regression. Outcomes from theoretical analysis of the data are used to provide further insight into how surface chemistry may be tailored to limit high-field leakage current in polyimides and insulating polymers in general.