Between July 30 and Aug. 7 four Cary fast-food restaurants have had their carbon dioxide tanks stolen. The gas is what gives pop its fizz.

Victims include Subway, 1373 Kildaire Farm Road on July 30; Ceci’s Pizza, 638 Cary Towne Blvd. F on July 30; Subway, 1813 N. Harrison Ave. on Aug. 7; and Firehouse Subs, 260 Grande Heights Drive on Aug. 7.

In every case the theft was discovered after a customer complained of flat soda or that the soda machine was not working.

The tanks are typically several feet tall and weigh hundreds of pounds and are stored behind the businesses.

On July 23 an oxygen cylinder for medical emergencies was taken from the food court at Cary Towne Center mall.

Police theorize that thieves are using the gas with welding torches to cut down metal so it can more easily be sold as scrap.

“It’s the only thing we can figure out that would use those combined,” said Capt. Mike Williams of the Cary police.

Cary businesses are not alone as victims. Three in north Raleigh and one in Durham have also been hit durng the same time period.