Penetration and Durability

• For deep penetration into wood decking, oil can’t be beat. Oil based deck stain creates a deep bond with the deck. The appearance of the stain when it is dried is even and smooth and it will wear very well. According to the Home Depot website, oil based stains are preferred for high traffic areas and for areas that are exposed to direct sunlight and rainfall. Water based stains will hold up to these challenges as well, but oil stains will last a bit longer under harsher conditions.
  
  

Moisture

• Water based deck stains are preferred by some because they will not trap moisture in the wood. Oil based stains do not “breathe” as well as water based stains and may lead to mildew and mold growth. When black spots appear on a deck it is often because mold and mildew is feeding on the resins in the oil based stains. Water based stains allow moisture to escape.
  
  

Adhesion

• The surface that you are planning to stain can help determine which type of stain to use. If you have a natural wood that hasn’t been stained before then oil will penetrate it well, but previously stained decks or decks that were painted in the past are not as well suited for oil-based stains. In these situations the water based stain is a better option because it adheres to previous coats on the deck.
  
  

Environmental Concerns

• There are some environmental concerns to think about when choosing a stain. Because of the potential moisture problem with oil-based deck stain, some manufacturers add toxic chemicals to the stain to kill mold and mildew before it can affect the surface of your deck. These algaecides and mother chemicals eventually rise to the surface of your deck and wash onto the ground or rub off on bare feet of your family or pets. Water based stains do not have to resort to these chemicals. Some states may not even allow the sale of stains with some of these chemicals in them. Check with your local authorities regarding what is allowed.
  
  

Application

• Oil stain goes on evenly and looks great with fewer coats than water based stain. But water stains are easy to work with and clean up easily. Oil stains take considerable time to dry and be ready for foot traffic, while water stains tend to dry quickly and are ready for use in just a few hours. Oil stains often have a strong odor that you’ll have to deal with during application while water stains have a lighter stench. Water stains also retain their color longer.