The pressure drop of glass-fiber and cellulose filter media loaded with oil-coated particles was investigated. The focus of this study was to develop a model describing the pressure drop of fibrous filter media under the above particle loading condition. A set of experimental data collected during previous work was used for this modelling. For the cases where the coated particles possessed an oil volumetric percentage below 50%, the filter was divided into two layers: One layer collected all test particles while the other layer remained clean, and the pressure drop of the first layer was estimated using a modified Bergman model, whereas that of the second was calculated with the Davies equation. The total filter pressure drop is the summation of the layers’ pressure drops. For the cases where the coated particles possessed an oil volumetric percentage above 50%, a power-law equation with two parameters (viz., the exponent, n, and the critical volume, Vcr) was applied to fit the experimental data. The correlations of the above parameters with the solid-core diameter fraction (X) of the particles and the viscosity of the coating oil were calculated for the glass-fiber and cellulose filter media.