The small village pumps don't have 91 anymore.
Interestingly the wise government decided to subsidize 91 to make a significant price difference which was marginal for many years. As 91 is good enough for scooters, lawn mowers etc. this might well lead to a shortage.
Overall the price difference was about 0.25 and now that:
The prices show the reverse side of the good exchange rates (weak THB) combined with rising oil prices. 95 now at about 1 EUR.