The valorization of vegetable oils (VOs) via the functionalization of their unsaturated groups has gained much interest. Epoxidation is the most common reaction for functionalizing VOs into promising polymers such as nonisocyanate polyurethanes and epoxy resins. From a chemical engineering standpoint, the use of esterified forms of VOs, i.e., fatty acid methyl esters (FAMEs), is recommended to ease their mixing due to the increased viscosity. To the best of the author’s knowledge, no kinetic models have been developed to compare the kinetics of epoxidation between VOs and their corresponding FAMEs. Kinetic models were developed using different analytical methods and considering the side reaction of oligomerization for the epoxidation of linseed oil (LSO), cottonseed oil (CSO), soybean oil (SBO), and their corresponding FAMEs using propionic acid and a solid catalyst, i.e., Amberlite IR-120. The model fits quite well with organic and aqueous phase experimental concentrations. The rate constants for epoxidation evolve in the following order: CSO > SBO > LSO. The linearity between the rate constant and the initial double bond concentration is more pronounced for VO-FAMEs than for VOs