Now, according to USA Today, the EPA won’t be awarding the production version of the Volt the same rating. The reason? That original formula had never received complete approval from the agency’s higher-ups and was eventually deemed to be misleading for consumers. The question then remains: How far can the Volt go on the equivalent of one gallon of gasoline? The short answer is that GM doesn’t know, or at least it doesn’t know how to translate its knowledge into a figure that will be comparable to gasoline-only vehicles on the road right now.

But neither does anyone else, including the EPA. GM has been partnering with the agency, other manufacturers and the Society of Automotive Engineers to come up with a formula that will provide consumers with a comparable figure. Until that happens, though, the Volt and the wave of electric vehicles headed our way will be bereft of fuel-economy numbers. That includes creations like the Nissan Leaf, Smart fortwo ED, MINI E and others.

Fortunately, the SAE claims to be close to a formula that will be workable, though the organization has yet to say much more than that it will publish details later this year.