Q:

Are Oreos vegan?

There are many contradictory sources on whether the classic black Oreo "Sandwich Cookies" are vegan or not.
Though sold almost worldwide, classic Oreos are produced in just a handful of big factories around the world by Mondelez/Nabisco/Cadbury/Milka.
Are all classic Oreos vegan?

A:

It depends.
The classic Oreo cookie is made using the same main ingredients, With some substitutions like in Canada, where the vegetable oil is coconut oil. None of these ingredients are currently of animal origin:

Sugar
Unbleached enriched flour (wheat flour, niacin, iron, thiamine mono-nitrate (vitamin B1), riboflavin (vitamin B2), folic acid)
High oleic canola oil and/or palm oil and/or canola oil
Cocoa (treated with alkali)
High-fructose corn syrup
Leavening agent (baking soda and/or monocalcium phosphate)
Corn starch
Salt
Soy lecithin
Vanillin
Chocolate
Palm oil

The contradictions seem to stem from the fact that the manufacturers themselves state that they are not vegan. According to the official UK site FAQ (emphasis mine):

No, Oreo have milk as cross contact and therefore they are not suitable for vegans.

However, some vegans including myself, and although I would rather buy products from brands that are entirely cruelty-free, would not deem them non-vegan solely because of cross-contamination risk.
This was different in the past as milk whey was used as an ingredient for the filling in the EU market.
The bottom line is: 
Ingredients of this heavily processed, industrialized snacks change often as they are always trying to reduce costs. Try to stay away from this gamble and if there isn't a choice, carefully read the ingredients on that particular package. Of course, also decide for yourself whether "might contain traces of milk" is acceptable.

