In Japan, fuel consumption accounts for 30% of truck operating cost, or more. As energy cost is rising, reduction of fuel consumption is of most vital importance. Among many elements which affect fuel economy of truck, there are, characteristics of engine, vehicle operating conditions, vehicle performance, and aerodynamics, and etc. In this paper, from standpoint of “vehicle performance”, consider ations are given to the fuel economy, and to the vehicle operating conditions in Asian typical countries, Japan and Thailand. Some interesting results were obtained, about relations between G.V.W. and vehicle performance. And strong clues were identified for reduction of fuel consumption, and instructions to drivers.