(WSJ) - Bartenders and waiters love to hear a wine drinker say, “I’ll have another.” Could the glassware they use make this happen more often?

Researchers at the University of Cambridge say it looks like larger wineglasses encourage patrons to drink more, even when serving sizes are held steady. A small study earlier this year in a local pub-restaurant found that wine sales were 9% higher when larger glasses were used to serve the same standard portion of 175 milliliters, or just under 6 ounces.

“It may be people perceiving the glass to contain less and drinking it faster,” said Theresa Marteau, director of the university’s Behavior and Health Research Unit, who led the research. Or it could stem from a phenomenon known as “unit bias,” meaning that drinkers judge the same volume of wine in a larger glass as less than a single portion, making them more likely to order another one.

Although small-scale, the study “tells us something is going on,” said Prof. Marteau, whose research focuses on how to encourage healthier behaviors. “Quite how large [the effect] will be when we roll it out into other contexts, we don’t quite know.”

Pub patrons in London found the results surprising. “I drink fast all the time because I’m a fast drinker,” said Rob Adam, a 22-year-old having a beer with colleagues. David Walton, a 42-year-old information-technology director, said he believed his pace of alcohol consumption was set by the fastest drinker in his group—usually a friend named Gus. “I call it the Gus effect,” he said.

Still, the research adds to a mounting pile of evidence, mostly in food, that “supersizing” portions, packaging or tableware leads to higher consumption. A recently published review found more than 70 studies on the topic and concluded that downsizing on all fronts could bring about a “meaningful” reduction in food intake.

One of the few other studies on alcohol consumption, by the University of Bristol, found that beer drinkers took more time over a pint presented in a straight-sided glass than a curvy one. That gives Prof. Marteau more confidence that the result of her wineglass study has legs.

She is aiming for a larger-scale trial involving several pubs, bars and restaurants across the U.K. One is already under way with a few more in the pipeline, she said. Her pitch is simple: It’s a “win-win” situation. “They want to find out what glasses might increase their sales, and we’re interested in what glass sizes might decrease them.”

James Hickey, general manager of the Pint Shop in Cambridge, where the first experiment was conducted, said “getting amazing data analyzed for free” outweighed the work of clandestinely switching the bar’s wine glasses.