Yes, you read that right. It's premium unleaded only in GM's mostly gasoline-free automobile. It seems a bit odd that The General would force its customers into using higher-priced gasoline if there wasn't a good reason for it, especially since it doesn't seem that the engine is highly stressed – 80 horsepower from 1.4 liters isn't exactly bleeding edge.
There is a possibility, however, that the car's engineers were able to wrestle a bit more efficiency from its constant-load engine/generator setup by using higher octane fuel. In any case, the automaker has not offered up any specific explanations on why premium is required... or, for that matter, what kind of fuel mileage the Volt will attain when the gasoline-powered engine is in operation.
We do feel compelled to point out that it probably doesn't really matter all that much that the Volt requires premium fuel considering how little gasoline the average user is likely to go through any given month, but still...
Your mileage may vary, indeed.
[Source: GM, The Truth About Cars]