Abstract: The selective removal of oil pollutants from aquatic environments using oil-absorbent materials is a common approach that balances treatment efficiency with oil recovery. Addressing the challenges faced by traditional oil-absorbent materials—namely, their inability to simultaneously satisfy the requirements of hydrophobic selectivity, reusability, and volume reduction after use—this study investigates the fabrication and oil-water separation performance of a highly hydrophobic, biodegradable gelatin-agarose-based composite aerogel. Gelatin and agarose were gelatinized and freeze-dried to form the initial aerogel, which was then subjected to surface roughening and low-surface-energy modification of the pore walls using ethyl orthosilicate and hexadecyltrimethoxysilane. The results showed that the modified pore walls formed an amorphous layer of silica-containing particles, increasing the water contact angle from nearly 0° to approximately 142° while maintaining rapid wetting of organic liquids. DSCM-1, with a porosity of 78.4%, exhibited the best oil absorption performance, with adsorption capacities ranging from 5.64 to 13.99 g·g⁻¹ for different oils and organic liquids; most low-viscosity liquids reached near-equilibrium within approximately 20 s. This aerogel can adsorb and remove both surface oil and high-density organic liquids beneath the water surface, with average recovery efficiencies of 99.5% and 91.1% for petroleum ether and diesel, respectively. After 90 days of burial in soil, the material’s mass loss rate reached 80.03%. The aerogel developed in this study combines selective oil adsorption, oil recovery, and biodegradability, and holds potential application value in the fields of marine oil spill cleanup and oil recovery.