Actually, you should consider yourself lucky, because S.C. has some of the cheapest gas in the country. State-wide, Georgia is usually cheapest in the U.S., and S.C. is close behind, along with Oklahoma and Missouri. Generally your cheap gas regions are the South and the “lower Midwest”. The West Coast and heavily urbanized areas (NYC, Chicago) tend to be the most expensive, for a number of reasons.
Gasoline is expensive in Cali because that state’s laws require the use of a specially formulated fuel. It costs a more to refine this stuff to begin with, and on top of that, if supplies are short, oil companies can’t just truck in gas from another state like they can anywhere else. So prices go up. This was a big problem in Cali earlier this year, when a couple of refineries unexpectedly closed due to fires, thereby cutting into supplies.
OTOH, delivery costs are pretty low in the South, because most of the oil comes from nearby (Texas or the Gulf).
Then there’s taxes. I don’t know what they are offhand in each state, but they’re definitely lower in S.C. than in Cali. (Notice that the next time you’re in North Carolina, gas is about 10c more. The difference is all taxes.)
Then throw in differences in the costs of environmental regulations, land, property taxes, labor, insurance… you get my point. There isn’t one thing that acocunts for the 40-cent difference, but six or seven things that each account for a few pennies.
And yes, I am manic about gas prices. FWIW, regular unleaded goes for about $1.549 near downtown Chicago. We have about six different taxes on gas here. Lemme guess… it’s about $1.089 in S.C., no? I paid .689 in Spartanburg about a year ago. Now that was cheap gas!