As I've mentioned before and want to clarify; barley has gluten, if you have gluten intolerance issues or Celiac Disease you cannot eat it, ever. If you think you have either of these conditions I urge you to get tested as that is the only way truly identify Celiac. If you do not test positive for Celiac Disease but feel that there is a gluten intolerance I urge you to work with someone as you go through an elimination diet.
All of the research I have found indicates that oats do not have gluten in them. However, they are frequently grown near wheat or processed in the same facility as wheat or transported with wheat. This means that cross-contamination is an issue. There are a few brands that are advertised as gluten free and these companies maintain separate gluten-free facilities if they happen to produce gluten-containing foods as well.
Gluten Free Oats LLC http://www.glutenfreeoats.com/
Gifts of Nature - http://www.giftsofnature.net/Home.asp
Bob's Red Mill - http://www.bobsredmill.com/home.php?cat=112
Chateau Cream Hill Estates - http://www.creamhillestates.com/en_order.php