Preheat oven to 350F. Grease and flour 13x9x2-inch baking pan; set aside.
Sift clour, baking powder, soda, salt, and cinnamon together onto wax paper; set aside.
Beat granulated sugar, brown sugar, and butter in large bowl. beat at medium speed until well blended. Add oil and beat until smooth. Beat in eggs, one by one, then continue beating until thick and light, 1 to 2 minutes at medium speed.
Add sifted dry ingredients and beat just enough to blend. By hand, mix in carrots and walnuts; batter will be thick.
Spoon batter into pan, smoothing to edges. Bake 50-60 minutes, until springy to touch and a toothpick inserted in center of cake comes out clean.