Oreos are considered vegan if manufactured in the United States. In some places in Europe, Oreos may contain whey and are not considered vegan. In addition, depending on the strictness of the vegan's principles, the sugar in Oreos may not be considered vegan.
The manufacturer of Oreos, Kraft Foods, has several suppliers. Some of the suppliers use sugar that is refined with bone char, a by-product of animal bone. Veganism is a diet that excludes all animal products. This includes meat, eggs, dairy and all other products derived from an animal. The strictest of vegans do not consume products with animal by-products, which would include items that are refined with animal ingredients, such as some sugars.