Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) cause extensive damage to many stored products, thereby reducing their nutritional and economic value. However, controlling these pests with insecticides can have an impact on the environment as well as on human health. Thus, it is important to identify more environmentally safe compounds, such as plant oils, that can be used as an alternative means of pest control. In this study, we investigated the toxicity of 5 plant oils isolated from lavender (Lavandula angustifolia Mill., Lamiaceae), onion (Allium cepa L., Amaryllidaceae), flax (Linum usitatissimum Mill., Linaceae), caraway (Carum carvi [Lindl.] H. Wolff, Apiaceae), and brown galingale (Cyperus fuscus, or saad L., Cyperaceae) for use on the stored-products insect pests T. castaneum and O. surinamensis. The efficacy of these oils was evaluated at concentrations of 1, 2, 3, and 4 µL per mL and at an exposure time of 24 h. Results indicated that O. surinamensis was more susceptible to plant oils than T. castaneum, which showed a greater resistance to these natural products. Results also revealed that caraway and lavender oils were the most toxic of all treatments rendered for T. castaneum, with 50% lethal concentration (LT₅₀) values of 1.2 and 2.4 µL per mL, respectively. The onion and lavender oils displayed the highest efficacy on O. surinamensis with insect mortality reaching 100% with onion oil and an LT₅₀ value for lavender oil of 0.6 µL per mL. These results suggest that onion, lavender, and caraway oils are potentially promising and environmentally acceptable alternatives for the control of T. castaneum and O. surinamensis.