In a letter written on Sept. 23, the E.P.A. says it will “initiate a new rule-making to explore in detail the information displayed on the current fuel economy label and the methodology for deriving that information.” The E.P.A. letter said consumer labels should “provide practical, usable and meaningful information to vehicle purchasers” interested in battery electrics, plug-in hybrids and “other advanced technology vehicles.”

The E.P.A.’s letter was in direct response to a Sept. 10 proposal from Rainier client ETV Motors, which is working on battery technology as well as a hybrid concept that uses a micro-turbine to replenish an electric vehicle’s batteries. ETV wrote to the U.S. agency because “the world needs the E.P.A. to take the lead. What the E.P.A. does will have a ripple effect into all markets.” The United States, says ETV’s CEO Dror Ben-David, “is a leader in rule-making.”

ETV proposed that consumers be given three pieces of information on electric vehicles: the E.V.’s all-electric range, its energy efficiency in electric mode (expressed in miles a 10 kilowatt-hours) and, for plug-in hybrids, its fuel efficiency when the internal-combustion engine kicks in.

Environmental writer and speaker Jim Motavalli writes about the situation on the Wheels blog on NYTimes.com.