The Transportation Energy Data Book: Edition 21 is a statistical compendium prepared and published by Oak Ridge National Laboratory (ORNL) under contract with the Office of Transportation Technologies in the Department of Energy (DOE). Designed for use as a desk-top reference, the data book represents an assembly and display of statistics and information that characterize transportation activity, and presents data on other factors that influence transportation energy use. The purpose of this document is to present relevant statistical data in the form of tables and graphs. This edition of the Data Book has 12 chapters which focus on various aspects of the transportation industry. Chapter 1 focuses on petroleum; Chapter 2 - energy; Chapter 3 -greenhouse gas emissions; Chapter 4 - criteria pollutant emissions; Chapter 5 - transportation and the economy; Chapter 6 - highway vehicles; Chapter 7 - light vehicles; Chapter 8 - heavy vehicles; Chapter 9 - alternative fuel vehicles; Chapter 10 - fleet vehicles; Chapter 11 - household vehicles; and Chapter 12- non-highway modes.