Trick-or-Treat Stevens
'The Lovely Michelle'
So if regular was the least expensive back then, you would think that JR would be offering that since he was trying to make it look like he cared about how people struggled with the price of gas!
I'm sure, even for a fictional fuel station, it would offer the leaded/regular fuel too. It just wouldn't be advertised as prominently since newer vehicles used the (newer for that time) unleaded fuels.
These older episodes are fun to watch to see how things like this have changed so much over the years.