Premium Fuel?

If the Volt is like the Prius, it also requires premium fuel. I attended a Toyota training class when I worked for Toyota.
I was told by the trainer, that the Prius had a higher compression engine (10.5:1).
This engine was used in other Toyota products as well with 9.0:1 compression.
The reason given, The higher compression lets the engine start quicker when changing from electric to gas. This helps the transition to be more seamless between the functions.