A nearly $18 Big Mac meal is creating a stir on social media

The magic of McDonald’s? You always know what you’re going to get. No matter which one you walk into — whether in Islip, New York, or Istanbul, Turkey — you can order a Big Mac and fries. And it will taste the same.

But will it cost the same? No.

Recently, Sam Learner was traveling on the Connecticut Turnpike when he discovered just how variable the prices can be. After pulling into a rest stop in Darien, Connecticut, he was astounded by the prices he saw on the McDonald’s menu. A Big Mac combo meal with fries and a soft drink costs $17.59. So he snapped a photo and posted it to Twitter.

MORE: McDonald’s Indonesia launches wedding packages with McNuggets

Why so expensive? Since about 90% of McDonald’s franchises are independently operated, the owners can set their own prices. If you own a McDonald’s at a rest stop along a highway (where people are hungry and in unfamiliar territory), you can charge more for the same product. Franchise owners in areas with a high per-capita income also tend to charge higher prices.

Learner did some more sleuthing and quickly followed this tweet up with a second one:

Unsurprisingly, Learner’s tweets sparked a lively Twitter debate about the economics of fast food.

“I downloaded the mcdonald’s app to check – same items are just about half the price less than 2 miles away at a different store,” commented Bad Gibbon @Mostlymonkey. “Wow, that is a hell of a convenience premium!”

Many people commented on the injustice of price gouging, with others urging people not to eat at McDonald’s anymore.

“Rest stops are literally highway robbery,” wrote Bella @imbellawonder.

But the most depressing response came from ednycinc44, who shared what McDonald’s prices were in 1972, when a Big Mac cost $.65 cents:

MORE: This recipe features McDonald’s Big Mac flavors in a salad