Flexible pavement comprises of multiple layers designed to adapt to traffic loads and environmental conditions. Bitumen, a key binder in flexible pavements, provides cohesion and waterproofing, ensuring durability and load distribution. The depletion of petroleum sources has resulted in increased bitumen expenses and limiting availability, hence reinforcing the necessity for an alternative binder. Bitumen undergoes degradation as it ages. With increasing rigidity and brittleness, it compromises with the performance of the pavement. Henceforth, there is a growing interest in recycling and rejuvenating the ageing bitumen pavements due to the increased emphasis on sustainable construction. Rejuvenators, including motor oil, waste vegetable oil, high-density polyethylene, thermoplastics, used tires, coal fly ash, diatomite powder, etc. have been found to be efficient in restoring the qualities of aged bitumen. This paper reviews the effectiveness of using waste oils to rejuvenate bitumen, focusing on the chemical interactions between the two and the subsequent enhancements in flexibility and durability. The studies indicate that waste oils can greatly enhance the bitumen's capability to withstand cracking at low temperatures and increase its durability under repeated stress. However, the effectiveness of this improvement depends on the type and dosage of the oil utilized. Issues such as the possibility of excessive softness, variations in the content of oil, and the requirement to optimize the amount of rejuvenator used are also discussed.