Internal combustion engines′ fuel economy is an important role for engine designers,engine manufacturers over the past 30 years,especially passenger car motor oils.In heavy duty diesel engine,over the past 20 years,fuel economy has in some cases been sacrificed for exhaust gas emission optimizations.Now,Heavy Duty Automotive and the related industries have strong interest in fuel economy and the lubricants.It is driven by competitive market forces as well as government mandates and new emission regulations.Japan was the first country in the world to establish and implement heavy duty trucks and buses fuel economy standards.Other countries also have followed either by establishing direct fuel economy standards or greenhouse gas(GHG) emissions standards which are directly tied to fuel economy.This paper is discussing that heavy duty diesel engine lubricants can contribute on fuel economy.The contribution of various aspects of engine oil formulations on fuel economy will be discussed such as lubricant viscosity grade,lubricant additives and friction modifiers.In this paper,the evaluation discussions are based on fuel economy measurements in some bench tests,standardized laboratory engine tests and field tests. Internal combustion engines’ fuel economy is an important role for engine designers, engine manufacturers over the past 30 years, especially passenger car motor oils. Heavy duty diesel engine, over the past 20 years, fuel economy has in some cases been sacrificed for exhaust gas emission optimizations. Now, Heavy Duty Automotive and the related industries have strong interest in fuel economy and the lubricants. It is driven by competitive market forces as well as government mandates and new emission regulations. Japan was the first country in the world to establish and implement heavy duty trucks and buses fuel economy standards .Other countries also have either followed either by establishing direct fuel economy standards or greenhouse gas (GHG) emissions standards which are directly tied to fuel economy.This paper is discussing that heavy duty diesel engine lubricants can contribute on fuel economy. The contribution of various aspects of engine oil formulations on fuel economy will be discussed su ch as lubricant viscosity grade, lubricant additives and friction modifiers.In this paper, the evaluation discussions are based on fuel economy measurements in some bench tests, standardized laboratory engine tests and field tests.