The topic of CO₂ and fuel consumption reductions from vehicles is a very broad and complex issue, encompassing vehicle regulations, biofuel mandates, and a vast assortment of engine and vehicle technologies. This paper attempts to provide a high-level review of all these issues.Reducing fuel consumption appears not to be driven by the amount of hydrocarbon reserves, but by energy security and climate change issues. Regarding the latter, a plan was proposed by the United Nations for upwards of 80% CO₂ reductions from 1990 levels by 2050. Regulators are beginning to respond by requiring ~25% reductions in CO₂ emissions from light-duty vehicles by 2016 in major world markets, with more to come. The heavy-duty sector is poised to follow. Similarly, fuel policy is aimed at energy diversity (security) and climate change impacts. Emerging biofuel mandates require nominally 5-10% CO₂ life cycle emissions reductions by 2020. Processes that utilize plant cellulose and waste products show the best intermediate term potential for meeting these goals, but long-term trends are towards biofeedstocks for refineries.Vehicle technologies are emerging to meet the regulatory mandates. Light-duty engine efficiency gains will result in about 30% fuel and CO₂ reductions by 2015. Many of the reductions will come from the use of direct injection technology in gasoline engines, and downsizing diesel and gasoline engines for more specific power. CO₂ savings shows a general linear relationship with cost. Diesel hybrids offer the greatest CO₂ reduction potential. Plug-in hybrids can lead to heavy electrification of the fleet for energy diversity and greenhouse gas reductions, but their CO₂ reductions are moderate and expensive. Battery performance is generally acceptable, but cost will be a recurring issue. Most light-duty efficiency technologies return money to the consumer over the life of the vehicle, so the CO₂ reductions also come with an economic gain to the owner.In the heavy-duty sector vehicle and operational improvements offer the best gains at 16 to 28% fuel reductions. Engine technology trends are indicating nominally 15% reductions using advancements in currently utilized technologies. Research is shifting to gasoline engines, wherein upwards of 20-25% CO₂ reductions might be realized. Heavy-duty hybridization is emerging for vocational and urban vehicles, and can offer a 2 to 4 year payback period.Black carbon reductions from vehicles can have a profound effect on GHG impact, accounting for upwards of ~20% of CO₂ reductions proposed by the Intergovernmental Panel on Climate Change (IPCC) by 2050.