Oats can even be cross-contaminated by gluten in the field because farmers frequently rotate their crops...a crop of wheat one year, a crop of oats the next, in the same field.
This is usually only a problem for people with celiac disease, and Lymies.
The only other issue with oats is that they contain a protein that is very similar to gluten called avenin. Only a small percentage of celiacs are sensitive to avenin. Of course, I'm one of them, so I can't eat gluten-free oats either. And I LOVE oats!