When substituting oats for a portion of the flour in a cookie recipe, you get to choose which kind of oats to use. Both rolled and quick oats are made by steaming and pressing oat groats until flat, and have the same nutritional value. Rolled oats -- also called old-fashioned oats -- are thicker with a more noticeable texture; quick oats are thinner and easier to blend into your batter. To substitute using rolled oats, add them a 1/2 cup at a time until moistened. Steel oats are not recommended for cookies because they are too hard, and instant oats have been pre-cooked and will turn to mush if used in cookie batter.

Whole rolled oats can replace up to 50 percent of the flour in a cookie recipe. Some flour is necessary because oats are heavier than white flour and don’t contain any gluten. Using no flour at all results in dried out, crumbly cookies. Oats are naturally sweeter than wheat flour, so use less sugar when substituting them in place of flour. Add extra leavening to combat the density of rolled oats when using more than 1 cup. To make the substitution, add an additional 1 1/2 teaspoons of baking powder per 1 1/2 cups of rolled oats used, in addition to the rising agent already called for in your recipe.

Substitute oat flour, made from quick or rolled oats, in equal measure for whole wheat flour. Oats are a naturally gluten-free grain, but be aware that most oat crops are cross-contaminated and contain enough gluten to affect those with sensitive allergies. It is possible to purchase gluten-free oats – check the label to be sure. To make your own oat flour, process rolled oats in a coffee grinder, food processor or food mill. Pulse until you have a grain-flecked powder. Whole-grain flours such as oat flour stay fresh longest when refrigerated.

It is possible to make a peanut butter cookie without any flour at all by substituting rolled oats, because the peanut butter serves as a natural binding agent. Gluten-free, no-flour peanut butter cookie recipes do not include flour or additional leavening, even though more than 1 cup of oats are used. Blend rolled oats with eggs, peanut butter, sugar and baking soda to make a flourless baked cookie. Non-bake cookies can also be made with peanut butter and rolled oats, using no flour.