If you’re taking a road trip soon, you may unknowingly overpay for gas in a “danger zone” along state lines.

In a study of 20 high-risk areas where factors can create wide border differences, GasBuddy found the price spread differed by an average of 44 cents per gallon between the two sides, or around $10 per tank.

In extreme cases, drivers can spend an extra $25 when refueling the tank on the more expensive side of the line.

“Generally, the price spread between states next to each other is the difference in state and local taxes, but can be enhanced if the two neighbors have different types of required gasoline from different regions,” said Patrick DeHaan, GasBuddy senior petroleum analyst. “Usually, traveling across state borders isn’t an event that sticks out to motorists who are usually busy taking pictures of the welcome signs, but gas prices can stealthily surge just by crossing over the state line.”

Read more: 10 cities where you’re most likely to overpay for gas

Here are the border towns with the largest difference in gas prices:

$1.70 per gallon

• Needles, CA
• Mohave Valley, AZ

$0.88 per gallon

• Manhattan, NY
• Jersey City, NJ

$0.84 per gallon

• Blythe, CA
• Ehrenberg, AZ

$0.58 per gallon

• Greenwich, CT
• Port Chester, NY

$0.52 per gallon

• Staten Island, NY
• Perth Amboy, NJ

$0.46 per gallon

• Girard, PA
• Conneaut, OH

$0.45 per gallon

• Temperance, MI
• Toledo, OH

$0.40 per gallon

• Philadelphia, PA
• Mount Ephraim, NJ

$0.36 per gallon

• East St. Louis, IL
• St. Louis, MO

$0.35 per gallon

• Liberty Lake, WA
• Post Falls, ID

To avoid overpaying, identify the best places to fill up before you leave for a road trip. You can easily look up prices along your route using free smartphone apps like GasBuddy.

Which “danger zones” would you add to this list? Tell us on Facebook and Twitter.

Buying gas from a station on this list is better for your car