Chefs choose the best substitute for oregano by thinking about the type of dish it is going to be included in and considering other similar herbs. Most major flavors work with several herbs and spices, and chefs can usually choose another common companion herb rather than a specific substitute. For example, oregano is often used in tomato-based dishes, but other herbs such as parsley, rosemary, and tarragon also work with tomatoes. Alternatively, the chef can use marjoram as a substitute, because it is in the same family of herb. Other herbs such as basil and thyme can also be used as a substitute.

Thinking about the specific dish and the flavors within it is one way to choose the best substitute for oregano. Chefs can substitute it for other herbs commonly used in the specific type of dish. Oregano is commonly used in sauces, like Bolognese sauce, which are tomato-based or in salad dressings. Dill, fennel, and tarragon can be used in both tomato-based dishes and salad dressings.

A universal substitute for oregano can be determined by thinking about herbs which have similar flavors. Marjoram is the most similar herb in terms of taste and genus of plant. The flavor of marjoram is slightly sweeter than and not as strong as oregano, but it is otherwise very similar. Three parts of marjoram can replace two parts of oregano in recipes. Chefs should add 1½ teaspoons of marjoram to substitute for 1 teaspoon of oregano.

Basil is a substitute for oregano that can also be used in most dishes. The flavor of basil differs from oregano more than marjoram, but the two can generally be interchanged. Tomato-based dishes are particularly suitable for the use of both herbs. Substituting basil is also particularly suitable for dishes involving potatoes or breads.

Thyme is another substitute for oregano which can be used in some dishes. Mediterranean dishes which include meat often use thyme, and thyme works well with many other herbs. Chefs can use thyme as a substitute in many different dishes, including those based on beans, bread, tomatoes, and potatoes. Thyme is also suitable for use in salad dressings.

Combinations of herbs can also be used as a substitute for oregano. Chefs may replace it with combinations such as basil and thyme in dishes based on tomatoes or potatoes. A mixture of marjoram and basil or marjoram and thyme can also be used in most other dishes. Experimentation with different combinations of herbs in different types of dish is an effective way of determining the best substitute.