Preheat oven to 375 F. Cream together the butter and sugars. Add the eggs and vanilla. If a separate bowl, combine the oats, flour, baking soda, salt and mix. Add that mixture to the butter mixture and mix well. Next, stir in the chocolate chips, marshmallows and oreos. Scoop out 1 1/2 to 2 inch balls and place them on a greased cookie sheet. Bake for 8-10 minutes.