I just read the manual above and 91 octane is RECOMMENDED. That means to me you can probably use 87 or 89 if not towing or mountains driving. JMG. Ed
91 minimum recommended, 87 absolute minimum.
The way that I understand it is...
If the owner's manual states that 91 octane fuel(gasoline) is RECOMMENDED then, other grades of fuel can be used(but, no lower than 87). Even though we know that lower octane gasoline(85-86) is available in higher altitude areas.
However, If the owner's manual states the 91 octane fuel or high is REQUIRED then, you must use that.