I think the answer is that the gas prices have been all over the place lately and different chains will change prices with different frequency. Some will change daily, weekly biweekly etc...
Adding on to this: The Gas prices on the turnpike/gsp rest stops are governed by the state and only change once per week, and usually are higher than those of gas stations off of the Turnpike/GSP.
I think it's other market factors: name brand vs. generic, whether there's a cash discount or not, highway vs local- towards NYC or away from NYC (towards NYC usually costs more). Also, in a rapid price changing environment, the turnpike is slow to change since their deal is they can only change weekly.
ShaulYaakov is on the money with that, but I want to continue along his train of thought:
- If an owner owns a chain of gas stations, he has better buying power, ergo better pricing
- Gasoline is highly correlated to the price of crude oil (since gasoline is a byproduct of crude oil), it also takes a couple of weeks to go from being crude oil to the gas pump. When a gas station (or a chain of them) gets a tanker of gas, it's price reflects the crude oil price of 2-3 weeks ago. As Oil drops in price, gas will drop too. But the gas station has to pay off the tanker truck it got last week, and that's a factor as well. So if I happened to get a new delivery, and that delivery is 25% cheaper, I can pass some of that savings on to the consumer. The price of Oil has dropped significantly since early october (about 30%) and average NJ gas price has dropped about $0.22 per gallon in the last month.
Here's AAA's gas price survey for NJ:
https://gasprices.aaa.com/?state=NJ - can't seem to find a yearly chart