[Overdrive]

That is extremely doubtful, Sok. And for that matter, with the inclusion of ethanol in a lot of today's fuel, it's even less likely that today's 91 is up to the task of minimum duty for the engine. In an emergency, you put whatever is available in your tank, shy of dieself fuel, but simply put: these cars were not meant to save us money at the pump.

Always use the highest octane available when it is available. At no time should one be putting a different octane fuel in the car when the recommended is available. That's basically what is in the owner's manual, which trumps any other arguments. If it's not meant to be used, it's not in the owner's manual.