This text presents the latest information on mobile, recalcitrant compounds in gasoline and the newly emerging compounds being developed for use in gasoline and other vehicular fuels. The use of some of these compounds has resulted from environmental regulations specifying the addition of oxygenates to gasoline and papers in this volume consider the chemical, geochemical, hydrogeological, and atmospheric behavior of oxygenates. Methods for investigation, detection,and remediation, and the multidiscipliniary approaches needed to meet the challenges posed by these compounds are also discussed.