Sparkling wines have become a popular beverage in recent years, and the production of these wines is subject to adulteration during fermentation. This study investigated the stable carbon isotopic composition (expressed as delta(13)C) of the wine and of the CO(2) bubbles produced during the second fermentation for a number of sparkling wines produced in different countries around the world. Carbon isotope ratio analyses were used to estimate the addition of sugar obtained from C(4) plants (sugar cane or corn). The average delta(13)C values of the Brazilian brut, demi-sec, and doux sparkling wines were -20.5 +/- 1.2 per thousand (n = 18), -18.1 +/- 1.3 per thousand (n = 9), and -15.8 per thousand (n = 1), respectively. These values were statistically heavier (more positive carbon isotope ratio values) than the average delta(13)C of sparkling wines produced in other parts of South America (Argentina and Chile, -26.1 +/- 1.6 per thousand, n = 5) and Europe (France, Germany, Italy, Portugal, and Spain, -25.5 +/- 1.2 per thousand, n = 12), but not statistically different from sparkling wines produced in the United States or Australia. The most likely explanation for differences in the carbon isotope ratios of wines from these different regions is the addition of C(4) sugar during the production of some sparkling wines from Australia, Brazil, and the United States. The isotopic composition of the CO(2) bubbles (delta(13)C-CO(2)) followed similar trends. The average delta(13)C-CO(2) of most of the Brazilian and Argentine sparkling wines was -10.8 +/- 1.2 per thousand (n = 23), indicating that the likely source of carbon for the second fermentation was sugar cane. Conversely, the average delta(13)C-CO(2) of most of the sparkling wines produced in Chile and Europe was -22.0 +/- 1.2 per thousand (n = 13), suggesting that a different sugar (most likely sugar beet) was most used in the second fermentation. It was concluded that in many cases, the carbon isotope ratios of sparkling wine and CO(2) bubbles can provide valuable information about the sugar sources.