Gas is likely mixed with cheaper Ethanol now. Depending where you live there's likely less taxes on Ethanol, too.

Ethanol has an Octane rating of 114%, meaning that you can run your engine with less fuel in the fuel/gas mixture, if your engine, pipes, fuel pump and rubber hoses are made for that.

Ethanol is pretty awesome in terms of HP output, but you have to reprogram the maps in the ECU to correctly use it. The timings of "how fast" Ethanol explodes inside your engine cylinders is also faster, meaning if you don't remap your ECU there's chances of backfire because the valves don't close fast enough. That means if you don't have a V-Tec or similarly digitally controlled valve steering you have to also modify your camshaft.

Source: Rebuild 3 cars and their engines to be fueled with Ethanol because I live near a race track with cheap access to Ethanol.

Edit: some gas stations in the past were using shitty additives to boost the ethanol mixture with toluols and methyl ethylene variants, so could also be that. They're really bad for your engine block. Like, reeeeally bad because their mixture is very unpredictable and varies too much for a proper ethanol ECU map.