I run 91 octane ethanol free in my 1996 Mini Cooper. It keeps the fuel system cleaner and dose not damage the seals in the SPI system.

6464, when you say rattling do you think it could be engine knock? 

I use premium in my '87 with a 1275 stock engine. If I could find ethanol free close by, I would buy it, but no such luck.

I want to update my findings. My mini is an SPI, my only car. I've been using premium since day one. I've been told that I've been wasting my money because it makes no difference. I switched to using regular for a couple of months now and discovered  with my style of driving; rattling with taking off. Not all the time. But is there. I am now switching to mid grade.

I use 93 octane 5% gasohol because: *No-ethanol premium is no longer available here close by. *my 1275 mini has ethanol -resistant carb parts and high compression.

However - If I could get 93 octane with no ethanol I would prefer it. Like my chain saws, mowers, etc the mini gets only intermittent use and ethanol is problematic in that setting.

way back in the 1964 when I was in 8th grade, I did a chemistry project distilling/fractionating sub-regular grade gas (Sunoco 190) and compared it to premium (Sunoco 260) . Looking back, the teacher was insane to let me boil 100 ml of gasoline in a glass flask in a room with 25 other kids, no matter that the heat source was an electric pad and not a flame.

The sub-regular grade gas had 3 % black tar. The premium was crystal clear.

6464s   What Alex says is spot on.

I've been running my stock 998 and mildly tuned 1130 on regular gas for a few years.....since prices went silly.  I don't notice any performance issues over the premium.  I do however fill the tanks with premium in the fall for hibernation.

It entirely depends on the state of tune of your engine, how you drive, whether your fuel system is ethanol proof, and whether you care about fuel consumption.
The A-series in standard form will run on anything - it harks back to the days of 2* and 3* petrol; anything we can buy now is better than what was available (sub-5* or avgas) in 1959-1980.

The higher the ethanol content, the worse the consumption is.  Somewhere around 3-4% worse for every 5% of ethanol content.

A std SPi will run on anything commercially available in the USA.

I've used Premium no-ethanol for years. It uses so little gas I figure it's worth the difference in price. Mine does have a skimmed head for higher compression, but I would run the Premium anyway. I don't know what ethanol would do for our old fuel systems, not gonna gamble.

Thanks Dan. By the looks of things, it seams everyone has gone electric and no one on this site uses gas any more.

It probably has more to do with your engine's compression ratio. Mine has a MG Metro engine with 10.5:1 compression ratio, so it gets premium. I suppose another consideration is where you live and what additives are in the different grades. How much ethanol? I have heard though not confirmed that premium has a preservative so you don't need to add stabilizer, which I use anyway so I know the gas won't go stale quickly.

That being said, I probably will have to drain my Mini's fuel in the spring as I was not able to drive it this past season due to medical issues.

(edited for fat-finger typos)

I have an SPI and have been using premium. Am I wasting my money?