Recognizing a need in cultivated hexaploid oat (Avena sativa L.) for a reliable set of reference single nucleotide polymorphisms (SNPs), we have developed a 6000 (6K) BeadChip design containing 257 Infinium I and 5486 Infinium II designs correspond ing to 5743 SNPs. Of those, 4975 SNPs yielded successful assays after array manufacturing. These SNPs were discovered based on a variety of bioinformatics pipelines in complementary DNA (cDNA) and genomic DNA originating from 20 or more diverse oat cultivars. The array was validated in 1100 samples from six recombinant inbred line (RIL) mapping populations and sets of diverse oat cultivars and breeding lines, and provided approximately 3500 discernible Mendelian polymorphisms. Here, we present an annotation of these SNPs, including methods of discovery, gene identification and orthology, population-genetic characteristics, and tentative positions on an oat consensus map. We also evaluate a new cluster-based method of calling SNPs. The SNP design sequences are made publicly available, and the full SNP genotyping platform is available for commercial purchase from an independent third party. O at is an important cereal crop grown throughout most of the world. In cultivated hexaploid oat, as in most other crop species, there has been considerable interest in developing efficient SNP genotyping methods to facilitate genomic discovery and molecular breeding. Discovery and application of SNPs in a hexaploid species is challenging due to the presence of homoeologous gene copies. Many putative SNPs are later found to be interlocus variants (homeo-SNPs), and true intralocus SNPs may be difficult to assay due to the confounding presence of homoeologous loci. Nevertheless, successful SNP assays in oat can be developed (Oliver et al., 2011) and a first-generation SNP array has been used to develop a physically anchored consensus map in oat (Oliver et al., 2013). The objectives of the present communication are to report the expansion of this SNP array, to evaluate its performance, and to formally announce its public availability. In addition, we report an annotation of the SNPs and the loci that they represent, we share lessons learned during the assay development, and we evaluate a new clusterbased method for calling SNP genotypes in a polyploid.