How do soda companies put carbon dioxide in beverages?

Carbon dioxide gas is actually bubbled thru cold water until it reaches a saturation level. The colder the water the more carbon dioxide it can hold. In reality just cold tap water temperatures are used but the gas is applied at pressure. If you raise the pressure on the water (usually done in a pressure vessel) and bubble carbon dioxide thru it you can reach higher saturation levels of CO2 which will be retained long enough for the carbonated sugar water to be put in the bottling line.