Hi Heng. On average, we change the oil in our fryers on a weekly basis. We also clean and filter the oil in each of our fryers at least once a day to ensure this oil meets McDonald’s Canada standards. Our fries have their own dedicated fryer and meat products like our McNuggets are not cooked in the same fryer. We should also note that McDonald's fries are cooked in 100% vegetable oil, so they are perfectly suitable for vegetarian diets. Thanks for asking.