The rapid population, industrialization, and urbanization increase have led to a multi-fold increase in automobiles, thereby increasing the demand for lubricating oil. Among the available lubricants, automotive lubricating oil (motor oil) accounts for 57% of global lubricant demand, which is used to lubricate vehicular engine’s metal parts, reducing wear and increasing engine efficiency. However, with usage, it degrades due to (i) oxidation, (ii) thermal breakdown, (iii) micro-dieseling, (iv) additive depletion, and demands alteration with fresh motor oil. This chapter aims to discuss the characteristics of fresh and waste motor oil. Besides, it extensively explains the impact of waste motor oil (WMO) on water bodies, marine life, soil, and human health due to illegal disposal to overcome high waste management costs. Furthermore, it also focuses on the WMO hierarchy and suggests different treatment methods based on the hierarchy. However, among the available treatment methods, pyrolysis has drawn notice due to its adaptability and product diversification. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2025.