Back in eastern New Mexico (in fact, in the heart of oil country), finding premium gas with an octane lever > 90 is virtually impossible. I’ve never found it in my hometown. In fact, my parents own a car that suggests using an octane-level of 91, but they’re forced to use only 90 octane-level gas (which i’m hoping is not that big of deal…)
But if I cross the border to Texas, it’s regularly 92 and sometimes 93.
Here in California, Bay area, I can’t remember exactly the numbers, but IIRC, 91 or 92 seems to be the norm.
And even in Europe, unless I was decieved, I often saw levels of 95 and higher. In fact, there was generally only one level of octane there - but apparently that’s due to different rating systems.
There are minimum octane ratings set by by the authorities having juristiction over your location. They vary from state to state and country to country.
Another thing that could be a factor is the elevation of where you buy the gas. For example, “regular gas” sold above about 5000 feet ASL may be only 85 octane or less (and the higher grades are shifted downward as well).