Oat is widely consumed by people with celiac disease (CD). Its safety has been disputed because two peptides from oat avenins can be recognized as T cell epitopes by some CD patients. Differential signals of gluten-specific monoclonal antibodies and in-vitro T cells to oat varieties have suggested the existence of differences in immunogenicity. We aimed to clarify the nature of such responses by cloning avenin genes from 13 Avena species. A single oat plant contained up to 10 avenin genes. Avenin proteins clustered in four groups of which two contained the two avenin CD epitopes. All Avena species examined harbored avenins of these two groups, and as a consequence all contained avenins with the two avenin-specific epitopes, which makes it very unlikely to find oat cultivars that are devoid of these sequences. The established gluten epitopes from wheat, rye and barley were not present in oat avenins; some variants with two and three amino acid substitutions occurred, but they were predicted not to resist proteolysis in the gastro-intestinal tract. Perfect recognition sites of antibodies R5 and G12 were also not present in avenins. Thus, their signals to oat should not be interpreted as differences in immunogenicity for CD patients.