Whether or not a cookie sheet needs to be greased depends on the recipe and the type of cookie sheet you are using. Those who cook with silicone baking liners or parchment paper, for example, do not need to grease their cookie sheets, because the food never comes into contact with a surface it can adhere to. When baking, it is important to understand when a cookie sheet needs to be greased and what products should be used to grease the pan correctly.
Check the recipe to determine if it is necessary to grease the cookie sheet. Most recipes will specify whether the sheet should be greased or left ungreased. If no specification is given, check the ingredients. Cookies with large amounts of butter, such as sugar cookies, do not need to be baked on a greased baking sheet.
Use unsalted butter, vegetable shortening or cooking spray to grease the bottom of the cookie sheet. Never use cooking oil, as it will burn in the areas between the cookies and will be very difficult to remove.
Spray cooking spray evenly along the bottom of the cookie sheet, or use a clean paper towel to spread a thin layer of shortening or butter on the cookie sheet.