十亿立方英尺/天（bcfd）：用来定义天然气容积率的标准单位。每天10亿立方英尺的天然气足以满足全世界家庭使用天然气的2%左右。每天60亿立方英尺的天然气相当于每天约100万桶石油当量。英国热量单位（btu）：btu是可用于测量任何类型能源的标准能量单位。一加仑汽油的能量含量约为12万英热单位。“quad”指的是一个万亿（1015）btu。在2018年能源展望中，每种石油产品（如汽油、柴油、液化石油气等）的btu能量含量基于其比能量密度。传统车辆：一种装有内燃机的轻型车辆，通常是汽油点燃式发动机或柴油压燃式发动机。传统的包括先进技术的车辆，如涡轮增压和“温和的混合”功能，如停止-启动发动机。焦耳：焦耳是一个标准单位，可以用来测量任何类型的能量。1埃焦耳=1018焦耳，大致相当于1万亿btu。发电效率：在一次能源发电中，有用能源的产出与能源的投入之比。发电效率通常因发电类型和地区而异，但风、太阳能光伏和水力发电的效率假定为100%。混合动力汽车：“全”混合动力汽车是一种轻型汽车，它有电池（通常是金属氢化物镍）和电动机，以及传统的内燃机。当踩下制动器时，移动车辆的能量存储在蓄电池中，可以在以后使用，从而节省燃料。氢燃料电池汽车：一种轻型汽车，其燃料为氢并储存在车上。氢通过一个燃料电池，燃料电池为汽车提供电力。轻型车辆（ldv）：道路车辆的分类，包括轿车、轻型卡车和运动型多用途车（suv）。摩托车不包括在轻型车队规模或燃油经济性中，但摩托车使用的燃油包括在轻型运输需求中。液化天然气：天然气（主要是甲烷），经过超冷处理后转化为液态，便于运输。液化石油气：碳氢燃料的一种分类，包括丙烷、丁烷和其它类似的低分子量碳氢化合物。百万石油当量桶/天（mbdoe）：根据与典型石油桶相关的能源含量，针对不同类型能源（天然气、煤炭等）的标准计量单位。每天100万桶的石油当量足以为当今世界道路上约4%的轻型车辆提供燃料。mbdoe中所有能源类型的报告都是在石油当量的基础上完成的，石油产品除外，石油产品是以实物桶报告的。天然气液体（ngl）：主要与天然气一起产生的液体燃料。天然气是天然气的组成部分，在天然气加工过程中，天然气从气态分离成液态。乙烷、丙烷、丁烷、异丁烷和戊烷都是ngl。经济合作与发展组织（经合组织）：一个论坛，来自世界各地的约35个国家相互合作，并与更多的伙伴国家合作，以促进将改善全世界人民经济和社会福祉的政策。插电式混合动力汽车（phev）：一种轻型车辆，通常使用电动机。与其他电动汽车不同，phev也有一个传统的内燃机，可以在需要时使用石油燃料为其电池充电，在某些情况下为汽车提供动力。购买力平价：购买力平价。一次能源：包括石油、天然气、煤炭、核能、水力、地热、风能、太阳能和生物能源（生物燃料、城市固体废物、传统生物量）。它不包括电力或市场热，这是反映一次能源转换/生产的二次能源类型。二次能源：从一次能源中获得的能源类型，包括电力和市场热。例如，电力是使用天然气、风能或其他一次能源产生的二次能源。万亿立方英尺瓦特：电功率的单位，等于一焦耳每秒。一座十亿瓦的发电厂可以满足美国50多万户家庭的用电需求。千瓦（kw）=1000瓦；千兆瓦（gw）=100000000瓦；兆瓦（tw）=1012瓦。瓦时：电能的单位。300太瓦时相当于1万亿btu（四倍）。千瓦时（kwh）=1000瓦时；千兆瓦时（gwh）=100000000瓦时；兆瓦时（twh）=1012瓦时。
billion cubic feet per day (bcfd): a standard unit used to define volumetric rates of natural gas. one billion cubic feet per day of natural gas is enough to meet about 2 percent of the natural gas used in homes around the world. six billion cubic feet per day of natural gas is equivalent to about 1 million oil-equivalent barrels per day. british thermal unit (btu): a btu is a standard unit of energy that can be used to measure any type of energy source. the energy content of one gallon of gasoline is about 120,000 btus. “quad” refers to a quadrillion (1015) btus. in the 2018 outlook for energy, energy content in btus for each oil product (e.g., gasoline, diesel, lpg, etc.) is based on its specific energy density. conventional vehicle: a type of light-duty vehicle with an internal combustion engine, typically either a gasoline-fueled spark ignition engine or a diesel-fueled compression ignition engine. conventional includes vehicles with advanced technologies such as turbocharging and “mild hybrid” features such as a stop-start engine. exajoule: a joule is a standard unit that can be used to measure any type of energy. 1 exajoule = 1018 joules, roughly equivalent to 1 quadrillion btus. generation efficiency: the ratio of useful energy output to energy input in the generation of electricity from primary energy sources. generation efficiency typically varies by generation type and region, however wind, solar pv and hydro are assumed to be 100 percent efficient. hybrid vehicle: a “full” hybrid is a type of light-duty vehicle that has a battery (usually a nickel metal hydride) and an electric motor, as well as a conventional internal combustion engine. when brakes are applied, the energy of the moving vehicle is stored in the battery and can be used later, thus saving fuel. hydrogen fuel cell vehicle: a type of light-duty vehicle for which hydrogen is the fuel and is stored onboard. this hydrogen is passed through a fuel cell that then provides electricity to power the vehicle. light-duty vehicle (ldv): a classification of road vehicles that includes cars, light trucks and sport utility vehicles (suvs). motorcycles are not included in the light-duty vehicle fleet size or fuel-economy, but the fuel used in motorcycles is included in light-duty transportation demand. liquefied natural gas (lng): natural gas (predominantly methane) that has been super-chilled for conversion to liquid form for ease of transport. liquefied petroleum gas (lpg): a classification of hydrocarbon fuel including propane, butane and other similar hydrocarbons with low molecular weight. million oil-equivalent barrels per day (mbdoe): a standardized unit of measure for different types of energy sources (natural gas, coal, etc.) based on energy content relative to a typical barrel of oil. one million oil-equivalent barrels per day is enough energy to fuel about 4 percent of the light-duty vehicles on the world’s roads today. reporting for all energy types in mbdoe is done on an oil-equivalent basis, with the exception of oil products, which are reported in physical barrels. natural gas liquid (ngl): a liquid fuel produced chiefly in association with natural gas. ngls are components of natural gas that are separated from the gaseous state into liquid form during natural gas processing. ethane, propane, butane, isobutane and pentane are all ngls. organisation for economic co-operation and development (oecd): a forum for about 35 nations from across the world that work with each other, as well as with many more partner nations, to promote policies that will improve the economic and social well-being of people around the world. plug-in hybrid electric vehicle (phev): a type of light-duty vehicle that typically uses an electric motor. unlike other electric vehicles, a phev also has a conventional internal combustion engine that can charge its battery using petroleum fuels if needed, and in some cases power the vehicle. ppp: purchasing power parity. primary energy: includes energy in the form of oil, natural gas, coal, nuclear, hydro, geothermal, wind, solar and bioenergy sources (biofuels, municipal solid waste, traditional biomass). it does not include electricity or market heat, which are secondary energy types reflecting conversion/production from primary energy sources. secondary energy: energy types, including electricity and market heat, that are derived from primary energy sources. for example, electricity is a secondary energy type generated using natural gas, wind or other primary energy sources. tcf: trillion cubic feet watt: a unit of electrical power, equal to one joule per second. a 1-gigawatt power plant can meet the electricity demand of more than 500,000 homes in the united states. kilowatt (kw) = 1,000 watts; gigawatt (gw) = 1,000,000,000 watts; terawatt (tw) = 1012 watts. watt-hour: a unit of electrical energy. 300 terawatt hours is equivalent to about 1 quadrillion btus (quad). kilowatt-hour (kwh) = 1,000 watt-hours; gigawatt-hour (gwh) = 1,000,000,000 watt-hours; terawatt-hour (twh) = 1012 watt-hours.