So, you're taking a road trip for the Fourth of July weekend, and you're about to leave the state.
Do you fill up on gas now, or do you wait to fill up after you cross the border?
Making the wrong decision could cost you more than $10 a tank, depending on where you're heading.
"Watch out for those state lines," says Patrick DeHaan, senior petroleum analyst at fuel-station-finding app GasBuddy.
Gas prices averaged $2.86 per gallon Tuesday, according to AAA, hitting a four-year high for Independence Day travel.
Here's some advice before you head out – all prices according to GasBuddy:
1. Fill up in Arizona, not California
The price disparity between these two states is extreme.
Arizona averaged $3.06 per gallon as of Tuesday, while California averaged $3.73, according to GasBuddy.
At those prices, a 15-gallon fill-up is $10.06 more expensive in California.
2. Fill up in Texas, not New Mexico
If you're road-tripping in the Southwest, price differences can be significant. This is another good example.
The price of fuel in Texas, where oil refineries are clustered, averaged $2.66 on Tuesday. In New Mexico, it was $2.91.
That means you'd save $3.75 in Texas on a 15-gallon tank.
3. Fill up in Louisiana, not Texas
But Texas is more expensive than Louisiana, which is also a hot spot for refineries.
Prices averaged $2.59 in Louisiana on Tuesday, compared with $2.66 in Texas.
Generally, though, "anywhere in the South" is a good place to fill up, DeHaan said. "They’re right in oil’s backyard. Plus, low taxes."
4. Fill up in Ohio, not Michigan
Ohio is much more forgiving on the pocketbook than its rival to the north.
With prices averaging $2.79 on Tuesday, Ohio was sharply lower than Michigan's $2.96.
5. Fill up in Virginia, not West Virginia
Going white-river rafting in West Virginia? Sounds fun.
But fill up first in Virginia, where prices are 21 cents lower at $2.61.
6. Fill up in West Virginia, not Pennsylvania
West Virginia doesn't look so bad when you see prices in Pennsylvania, which averaged $3.01 on Tuesday, compared with West Virginia's $2.82.
7. Fill up in Massachusetts, not Connecticut
At $2.91, Massachusetts isn't exactly an oasis of cheap gas.
But it's still cheaper than neighboring Connecticut at $3.08.
8. Fill up in South Carolina, not North Carolina
North Carolina is 14 cents higher at $2.66.
Come to think of it, fill up in South Carolina no matter where you're heading. It's the cheapest gas state in the country, according to GasBuddy.