<p>This review explores the synthesis of biomass-derived carbon soot from used oils, including waste edible and engine oils, and its potential as electrode material in high-performance supercapacitors. With the growing environmental challenges related to the disposal of waste oils, such as used cooking oils, there is an urgent need for sustainable recycling solutions. The paper emphasizes the reusability of biomass-based oils, highlighting various synthesis techniques for biomass-derived carbon soot, including physical and chemical activation, heteroatom doping, and composite formation with transition metals and polymers. These approaches aim to enhance the electrochemical performance of soot-based electrodes. The review focuses in particular on the structural modification of carbon nanomaterials—such as graphitization, surface area, pore size distribution, and heteroatom content—key factors in optimizing supercapacitor performance. In contrast to more widely studied soot sources like candle and engine soot, biomass-derived soot offers a novel, less explored alternative for energy storage applications. The paper provides a comparative analysis of different soot types, emphasizing the environmental benefits of converting waste biomass oils into valuable carbon materials. It concludes with recommendations for future research, including refining synthesis methods, optimizing electrochemical properties, and integrating biomass-derived soot with advanced materials like metal–organic frameworks. This approach aligns with the principles of a circular economy, advancing sustainable energy storage technologies.</p>