Arrange 12 six-inch corn tortillas in a single layer on two rimmed baking sheets; brush both sides of each tortilla with vegetable oil (about 2 tablespoons per tray).
Place a wire rack upside down on top of the tortillas to keep them flat. Bake on the upper- and lower-middle racks of a 450-degree oven until lightly browned and crisp, 15 to 18 minutes, switching and rotating sheets halfway through baking.