Preheat oven to 375°F Brush bottom and sides of an 8-inch round cake pan with oil; line bottom with a round of wax or parchment paper, and brush paper with oil.
In a large bowl, whisk together oil, eggs, 1 cup sugar, and orange juice until smooth. Add flour, cornmeal, baking powder, salt, and orange zest; whisk gently to combine.
Pour batter into prepared pan; sprinkle top evenly with remaining 1/3 cup sugar (topping will be thick). Bake until cake begins to pull away from sides of pan and a tester inserted in center comes out clean, 35-40 minutes.
Cool in pan 20 minutes. Run a knife around edge of cake; invert cake gently onto a plate, and remove parchment paper. Re-invert cake onto a rack to cool completely. Serve with orange segments, if desired.