Many nations have issued exhaust emission regulations for internal combustion engines not only for on road but also for off-road vehicles. In these regulations, several new exhaust gas sampling systems have been applied such as the direct sampling method (ISO 8178 / EPA Part.90 / EPA Part. 91) and a revised methods from the existing regulation (SAE J 1088). The sampling method is a particularly noticeable change. Though we understand the necessity of having different regulations for different application engines, and have introduced several types of gas sampling systems for our analysis work, we expect to establish a common test procedure because we produce a wide range of different application engines for motorcycles, personal water crafts (PWC), all terrain vehicles (ATV) and small utility engines. We compared details of the emission data obtained from different sampling systems. This paper describes that the difference of the observed NOx data from several different sampling systems was minimal and a common gas sampling system could be applied to these regulations at least for the fundamental exhaust emission study.