Preheat oven to 350 degrees F. Grease bottom of a 13x9 inch pan. Beat cake mix, water, butter, and egg whites in a large bowl on low speed for 30 seconds, then on medium speed for 2 minutes. Crush Oreo Cookies and mix into batter.
Pour batter into the pan.
Bake for 33-38 minutes, or until a toothpick comes out clean. Let cake cool for 10 minutes before you enjoy it!