As salaamu alaikum,
Of the Nabisco Oreo products, the following two contain animal derived ingredients is confirmed by the associate director of customer affairs of the company. Most likely it is the mono and diglycerides that are animal derived from these 2 products because after looking over the ingredients labels only these 2 products contain mono and diglycerides.
These 2 products are:
-Oreo Reduced Fat varieties
-Oreo Sugar Free varieties
So basically, eat the fatty oreos and you're good to go =)