This is the most common form. Rolled oats are groats that have been heated and pressed flat with steel rollers so that they can cook quickly. Rolled whole oat groats are sold as old-fashioned oats or large flake oats and cook in about 5 minutes.
Quick cooking oats are sliced before heating and pressing and cook in about 1-3 minutes, depending on the size of the slices (coarse, regular to fine). The smaller sized ones take less time to cook.
Instant oats have been pre-cooked, dried and pressed very thin and only require the addition of boiling water to form a very smooth hot cereal. Instant oats often contain added salt, sugar, flavourings and colours and are not a healthy choice.