Cut potatoes lengthwise into 1/3-inch-thick slices, then cut into 1/3-inch-wide sticks. Immediately toss with oil, salt, and pepper in a large bowl, then spread sticks in 1 layer in a large shallow (1-inch-deep) baking pan.
Bake in lower third of oven 15 minutes. Loosen potatoes from bottom of pan with a metal spatula, then turn over and spread out again. Bake until crisp and golden brown on edges, about 10 minutes more.