Question came up when talking to my Dad, who uses premium petrol in his cars.

For the varietals available in KL (and in the UK), almost certainly no. Most of the guidance I found in various forums online indicate that you should use the grade recommended for your car (Quora, Yahoo Answers and beyond).

For my Dad’s car, a 4 year old Merc, the manual recommends “high” octane fuel – i.e. 91 grade or above. The ‘low’ octane fuel available here is 95, the high 97 (at a 25% additional cost premium), so the 95 should be fine for him. I think its a similar situation in the UK.

As I understand it the octane number indicates the fuel’s combustibility, with higher octane fuels being less ‘explosive.’ Net issue, if you use a lower octane number in an engine tuned for high octane fuel, you can throw the timing off as presumably the combustion takes place faster than it should. The reverse doesn’t sound like its as much of an issue, so it doesn’t hurt to use the high octane fuel – but it isn’t necessarily worth the money.

In short, use what’s recommended for your car!