Can brown sugar be substituted for granulated sugar in oatmeal cookies?

Yes, brown sugar can be substituted for granulated sugar in oatmeal cookies. It will add a richer flavor and a slightly chewier texture due to its molasses content. You can use a 1:1 ratio for the substitution, but keep in mind that the cookies may spread less and have a darker color. Adjusting the baking time may also be necessary for optimal results.