Preheat oven to 350°F. Grease a 13x9 inch baking pan.

Combine cake mix, vegetable oil, eggs and sour cream in a large bowl. Beat 2 minutes with a mixer at low speed, scaping sides of bowl frequently.

Mix sugar, cinnamon and walnuts in a medium bowl.

Spread half the batter in pan. Sprinkle half the walnut mixture over top. Repeat with remaining batter and walnut mixture.

Bake 40 minutes, or until a wooden toothpick inserted in the center comes out clean. Serve 20.