A vehicle's performance depends greatly on the operating conditions, such as journey type, driving behavior etc. Driving patterns vary with geographical location and traffic conditions. In today's global economy where automobile industries are concerned with both local and international markets, it becomes necessary to investigate vehicle performance for driving cycles of different countries and develop vehicle designs which are appropriate to the consumer's market. This paper concentrates on the issues related to designing hybrid electric vehicles. A method of optimizing the size of the principal hardware components of hybrid vehicles such as, electric motors, internal combustion engines, transmissions and energy storage devices based on the demands of different drive cycles is discussed in the paper. Driving cycles of five major countries around the globe were used for investigation: the ECE 15 used by United Nations Economic Commission for Europe (UN/ECE), the Japanese 10-15 mode, China's Beijing-11, Australian urban drive cycle and finally, the United States EPA75. The ‘V-ELPH 2.01’ EV-HEV computer simulation package developed at Texas A&M University was used for simulation testing.