Preheat oven to 350F. Spread sesame seeds on a shallow baking tray and bake, shaking frequently, until fragrant, 3 to 10 minutes. Do not brown. Cool.
Put sesame seeds in a blender or food processor fitted with the metal blade. Add vegetable oil. Process to a smooth paste, about 5 minutes. Add more oil if necessary, to bring the paste to a thick pouring consistency. Tahini will keep stored in a tightly covered jar in the refrigerator for several months. Makes 3 cups.