The increasing demand for alternative energy feedstocks is pushing many stakeholders toward the development of new processes, technologies, regulations, as well as new production and economical models. Waste oils represent a consolidated source of valuable raw materials for many industries and, as in the case of used vegetable oils, fit well with the medium- and long-term sustainability objectives of industrialized countries. Waste oils are transversal to many value chains, such as food, the plastic industry, and fossil fuel extraction
thus, they could represent precious raw materials if properly exploited. In this context, a state of the art is provided, which covers technical, regulatory, and research aspects of the topic.