ACEEE's scorecard draws heavily on data supplied by the Energy Department and the Environmental Protection Agency.

FORBES: Greener Than Thou

"The most simple definition is: achieving the same energy service with less energy commodity, " says Bill Prindle, deputy director of the American Council for an Energy-Efficient Economy (ACEEE), an independent nonprofit organization.

FORBES: Greener Than Thou

The Green Book, produced by the American Council for an Energy-Efficient Economy (ACEEE), says that in evaluating plug-in hybrids, it considers both the emissions from the gas engine and from the power plants that feed the grid.

FORBES: Green car book disses the Chevy Volt, GM isn't too happy