Preheat the oven to 275°. Set a rack on each of 2 baking sheets. In a bowl, toss the sweet potato slices with the oil and season with salt and pepper; make sure each slice is coated with oil. Arrange the slices in a single layer on the racks. Bake for 45 to 50 minutes, rotating the sheets halfway through baking, until the chips are deeply golden. The chips will crisp as they cool.