The Verdict Is OutUnsurprisingly, car makers tend to be a little over-enthusiastic about their products. This goes for electric car makers too, and when they quote electric driving range figures, they tend to be significantly higher than what the EPA's testing shows. That's why, for example, Nissan used "100 miles" in most of its communications about the LEAF and the official EPA number turned out to be 73 miles. It doesn't mean that you can't get 100 miles or more in the real-world, because its been done, but that's not a very conservative number.
The same seems to apply to the Tesla Model S. The company first said that it would have a 300 miles range with the biggest battery option (85kWh), and later even said that they had underestimated things and 320 miles was to be expected. So what's the official EPA number?
The first thing before we get into it is a disclaimer: The EPA's methodology to test electric vehicles doesn't tell you nearly as much as the equivalent tests done on gasoline cars. Gasoline is pretty much gasoline, but electricity can come from very clean sources (solar, wind) or very dirty ones (coal), and how you drive an EV can arguably have even more impact on its energy efficiency and range than with a gas car. So the environmental impact of driving an electric car will vary a lot more than a gas car, though even the worst case scenario (charging with coal) tend to be close or slightly better than burning gasoline in an internal combustion engine.
Anyway, so the EPA numbers are:
-89 MPG-equivalent combined
-88 MPGe in city driving
-90 MPGe on the highway
This gives the Model S an official EPA driving range of 265 miles, which is about 17% lower than the 320 miles estimate by Tesla. That's a smaller difference than Nissan's estimate vs the EPA, so we can say that Tesla wasn't doing too bad.
This 89 MPGe number puts the Model S behind most of the other commercial EVs on the market (the Mitsubishi i-MiEV at 112 MPGe, the Ford Focus Electric at 105 MPGe, and the Nissan Leaf at 99 MPGe), but the Model S is a different beast. It's bigger and more powerful, as well as more practical (under the hood is a huge trunk), which is bound to have an impact on energy-efficiency.