The direct conversion of natural products to useful engineering materials is desirable from both economic and environmental considerations. We are describing the synthesis and properties of 100 % oil-based epoxy resins generated from three epoxidized oils. The catalyst, tris(pentafluorophenyl)borane (B(C6F5)3) in toluene, allowed for controlled cationic polymerization at a very low concentration. Epoxidized oils (derived from triolein, soybean, and linseed oil) had varying epoxy content, rendering resins of different cross-link density. The polymerization was carried out at room temperature followed by post-curing at elevated temperature to speed up conversion. Epoxy resins were amorphous transparent glasses with glass transitions below glass transitions and hard rubbers above. Despite their high cross-link density, these materials show relatively low Tg’s reflecting the aliphatic nature of fatty acids and the presence of plasticizing “dangling” chains. The structure of the triglyceride starting oils influenced the properties of the resulting materials: the more regular structure of triolein compared to the very heterogeneous structures of soybean and linseed oils seemed to have enhanced some properties of the polymer networks. These epoxy polymers are potentially useful as encapsulating and potting compounds for electronic applications.