The use of hybrid electric vehicles (HEVs) as an alternative to traditional petroleum-powered cars has risen due to climate change, air pollution, and fuel depletion. The transportation sector is the second largest energy-consuming sector that accounts for 30% of the world's total delivered energy and about 60% of world oil demand. In 2008, the transportation sector accounted for about 22% of total world CO2 emissions. Within this sector, road vehicles dominate oil consumption and represent 81% of total transportation energy demand. This review discusses opportunities to reduce energy consumed and greenhouse gases in this sector and briefly discusses the Hybrid electric vehicles as a solution to improve fuel economy and reduce emissions. Also, the Classification of Hybrid Electric Vehicles, and the General architectures of hybrid electric vehicles and their subtypes have been discussed. Hybrid electric vehicle system components, system analysis, and fuel economy benefits are also explained. As the comparison results proved that the benefits of improved engine thermal efficiency outweigh the losses caused by longer energy transmission paths and showed that hybridization can improve fuel economy by about 24% in typical urban cycles. This study offers a thorough analysis of hybrid electric vehicles, including information on the designs, and energy management systems, created by different researchers. According to the thorough analysis, the current systems can execute HEVs rather effectively, but their dependability and autonomous systems remain not satisfactory. Several variables, difficulties, and issues related to the future generation of hybrid cars have been highlighted in this research.