Last updated: Jun 07, 2016

Next time you have trouble ordering just one red wine at the bar, blame your glass. A new study published in the journal BMC Public Health finds that people drink substantially more wine when it’s served in a big glass.

Researchers from the University of Cambridge in England studied the wine sales at a local pub, The Pint Shop, for about five months last year. Every two weeks, the bar owners switched out the glasses between the restaurant’s standard size (300 ml), larger glasses (370 ml) and smaller ones (250 ml).

Offering exactly the same amount of wine, but in a bigger glass, seemed to have a large effect on sales. When standard vessels were swapped for larger ones, vino sales went up 14.4% in the bar area and 8.2% in the restaurant portion of The Pint Shop.

This isn’t the first study to show that containers play tricks on our brain. A 2015 Cochrane review found that larger tableware increases how much people consume. But it is the first to look at alcohol—and the researchers have some interesting guesses into why a large glass leads to more rounds.

One possibility: people may think they got stiffed on a pour. “There’s some evidence to suggest that people consume more rapidly when they perceive that there’s less,” says Professor Theresa Marteau, director of the Behaviour and Health Research Unit at the University of Cambridge and the study’s senior author. The illusion of a small pour could lead people to drink faster.

Another theory is that people consume food and drink in units of one. “They think, ‘Oh, I’ll just one glass of wine, one slice of cake, one cup of coffee,'” Marteau says. When a wine portion looks meager, it may register as not a “full glass”—the perfect justification for another round.

Or maybe people just really love big glasses. “People say the nose or the bouquet of the wine is greater in a large glass,” Marteau says.

To find out for sure, the team is following up with more wine drinking experiments, in which they’re videotaping people drinking wine out of various glasses to compare drinking speed and satisfaction. Like so many other questions, the answer to this one lies at the bottom of a wine glass.

This article originally appeared on Time.com.