The requirement of meeting the emission standards for low emission vehicles (LEV) and ultra low emission vehicles (ULEV) has resulted in a more stringent examination of all elements of the automotive internal combustion engine that contribute to emission formation. The fuel system, as one of the key elements, is the subject of renewed and expanded research in an effort to understand and optimize the important parameters. Only through such enhanced understanding of the basic processes of fuel injection, metering, atomization, targeting, pulse-to-pulse variability and induction of fuel under cold, normal and elevated temperature conditions can the very low emissions of today's vehicles be further reduced to ULEV values.In the quest for reduced emissions and enhanced transient response, the electronic fuel injection system with sequential fuel pulse width control has become the fuel system choice in automotive gasoline engines, and this paper provides a comprehensive review of the research and development work associated with these systems and the associated basic processes. Various classes of port fuel injectors and their resultant spray structures are discussed, and the liquid fuel breakup mechanisms are reviewed. The key parameters that are required to numerically characterize a fuel spray from an automotive port injector are discussed, and the recent research advances are noted. The principal technologies that are available for enhancing the spray formation processes are reviewed, and the effectiveness of each technique is discussed. The effects of fuel spray parameters on engine performance are considered and evaluated from both the current state of knowledge and the research and development needs for the near future.