weird or not !
my au 4ltr ! i have been using mobil 98 ron petrol and getting this approximate mileage .
98 ron ! 120 klms per 1/4 of a tank price $ 1.32 per ltr
95 ron ! 120 klms per 1/4 of a tank price $ 1.29 per ltr
regular! 150 klms per 1/4 of a tank price $ 1.16 per ltr !!
how and why would my car use less fuel running on regular compared to high octane fuels.
i have always had bad idle issues in my car since i purchased it but even that has seemed to have almost stopped since using regular fuels ! and the other thing i noticed is that the exhaust note seems to be a lot quieter ! and my driving style has not changed at all ! and no highway use.
is this possible or am i dreaming.

If it's a stock engine then not so surprising, if it's a higher compression engine then I'd be disappointed.

It could be due to the higher octane grades having ethanol in them. 30k is a fair difference. Where they all filled from the same station?

yep ! same station ! regular fuel made my cars engine a lot quieter and slower off the mark !
when putting your foot down at a set of lights the engine just seemed to lack poke ! maybe that was one of the factors as i could not accelerate as much as usual.