Combine flour, sugar, and soda in a large mixing bowl, and set aside.
Combine butter, oil, water, and chocolate syrup in a medium saucepan; bring to a boil, stirring constantly. Gradually stir into flour mixture. Stir in buttermilk, eggs, and vanilla. Pour into a greased 15- x 10- x 1-inch jellyroll pan.
Bake at 400° for 20 minutes or until a wooden pick inserted in center comes out clean. Cool completely, and spread with Chocolate Frosting.