Not entirely true. Years ago stations had 3 tanks - one being dedicated for 89.. But since pumps became computerized/automated, and that software/hardware has become more and more reliable, "most" gas stations have switched to modern dispensers that blend the low octane and high octane on the fly (at the correct ratio) to get 89 "midgrade." They then "converted" the old 89 tank into another 87 tank - as that's the type of gasoline they sell the most of. An easy check to do over time is pay attention to what's available at your favorite gas station(s). If 93 is sold out, but 89 is still available, that likely = the station still uses a dedicated tank for "midgrade." Likewise if 87 is sold out, but 89 is still available. If 89 is sold out, along with either 87 or 91-93, it's blended while you're pumping, and isn't sitting stagnant. Just FYI.