Update (06/15/2011): I was just told, and just reviewed the ingredients. In Europe, and possibly elsewhere abroad, Oreos contain whey powder which is definitely NOT vegan. Boooooo!
Answer: it depends on your stance on refined sugar.
Backstory: a few years ago, Kraft, the maker of Oreo Cookie sandwiches bought out Hydrox Cookies and reformulated their Oreo cookies. They removed all dairy elements, and with a serious glance, the ingredient list looked vegan (unlike Soft Batch Cookies that switched their packaging to include “dairy flavors,” sigh). Vegans of the world rejoiced and began dipping seriously into their collective soy/rice/almond/hemp/… milk glasses. But some vegans questioned the sourcing of the Kraft sugars. One of those vegans is Vegeta-Lou. She contacted Kraft and just got word back. You can read the full emails here, but I’ll give you the summary.
Kraft has several sugar suppliers. Some of our suppliers DO use the animal-derived natural charcoal (also known as “bone char”) in their cane sugar refining process and some suppliers DO NOT use this process.
There you have it. The ingredients are all vegan, but the processing of their sugars can involve bone char.
Now you know! Thanks to Vegeta-Lou for sending us the info. Her website makes me want to get back to Paris. Thanks Lou!