Preheat oven to 350 degrees F (175 degrees C). Grease and flour one 13x9 inch pan.
Beat cake mix, mashed bananas, oil and eggs with an electric mixer on low speed for 30 seconds. Increase speed to medium and beat for 2 more minutes. Pour the batter into the prepared pan.
Bake at 350 degrees F (175 degrees C) for 33 to 36 minutes or until a toothpick inserted near the center comes out clean. Let cake cool then frost with your choice of frosting, if desired.
