Position a rack in the lower third of the oven and preheat the oven to 350 degrees. Grease and flour the pans or line the loaf pans with parchment.
Mix the flour, baking powder, and salt thoroughly and sift together onto a piece of wax paper. Set aside.
In a large mixer bowl (with the whisk attachment if you have a choice), beat the sugar, oil, and orange zest until well blended. Add the eggs one at a time, beating well after each addition. Continue to beat until the mixture is thick and pale, 3 to 5 minutes. Stop the mixer and add one-third of the flour mixture. Beat on low speed just until blended. Stop the mixer and add one half of the sherry. Beat just until it is blended. Repeat with another third of the flour, followed by the remaining sherry, and then the remaining flour.
Scrape the batter into the pan(s). Bake until a cake tester comes out clean, 50-60 minutes for either the tube pan or the loaves. Cool the cake in the pan(s) on a rack for about 15 minutes. Slide a skewer around the tube then slide a thin knife around the sides of the pan(s) to release the cake(s). Invert the pans and invert again, setting the cake right side up on a rack to cool completely.