The spring is naturally carbonated. Both the water and natural carbon dioxide gas are captured independently. Then in the bottling process, the carbon dioxide gas is added so that the level of carbonation in bottled Perrier is the same as the water of the Vergèze spring. Perrier is available in Europe in one liter, 750 ml, and 500 ml bottles, and in 33 cl cans. Most Perrier bottles are green and all have a distinctive 'teardrop' shape. In August 2001, the company introduced a new bottling format using polyethylene terephthalate to offer Perrier in plastic, a change that took 11 years to decide which material would best help retain both the water's flavor and its purported «50 million bubbles. Perrier comes in five flavors. Unflavored, lemon, and lime are the oldest flavors. In 2007, Citron Lemon-Lime and Pamplemousse Rose (Pink Grapefruit) flavors debuted.