Biodiesel is an important biomass, largely employed in the transport sector and produced from vegetable oils. Additionally, waste cooking oils may be reused to produce biodiesel fuel, minimizing environmental pollution. A laboratory experiment that affords a widespread way to discuss degradation concepts and tools for used vegetable oil characterization is presented. Through evaluation of the edible oil composition from distinct origins (oilseeds, heating types, and local community), an analytic evaluation of the composition and byproducts and a discussion about handling and storage of used vegetable oils was completed. For this purpose, nuclear magnetic resonance analysis was employed as an analytical method to access the waste cooking oil profile and explore the advantages of this versatile and practical spectroscopic technique.