Scientific research suggests that diet soda, or Diet Coke in particular, produces more carbonation or fizz than its counterpart, regular Coke. One scientist from Illinois State University tested the amount of CO2 that is released from soda using ultrasonic energy. Results showed that Diet Coke had more fizz.
The OSU College of Engineering offers several ways to test the fizz factor of sodas. One method is to shake various brands of soda to determine which soda produces the most spray. Another approach is to insert a balloon over a bottle of soda, shake the soda and measure the diameter of the balloon.
A final experiment involves connecting a tube to a soda-filled bottle. Place the tube inside an inverted cylinder that is filled with water and is also sitting in a water-filled tub. Shake the bottle, and the CO2 that is released displaces the liquid inside the cylinder for the purposes of measurement.