[wjones14]

When my daughter bought her 2003 Mini Cooper, I didn't realize that 91 Octane was recommended until we read the owner's manual. I emailed Mini, asking if it would hurt it to run 87, and their reply was:

"MINI Division requires the use of premium fuel (91 AKI) only if you want to duplicate the official EPA certified emissions and fuel economy. However, if you choose to use less then 91 AKI (it is not recommended to use below 87 AKI), it will not harm the engine. It is important to note that there will be a reduction in fuel economy and performance and emissions will increase."

So, with a reduction in fuel economy, it might cost nearly the same in the end to use 87 or 91 - so if that's true, it's pretty much a no-brainer to use 91.