Methods and compositions for assessing CpG island methylation are provided. Specifically, the invention provides an unstructured nucleic acid (UNA) oligonucleotide that base pairs with, i.e., hybridizes to, CpG islands. The subject oligonucleotide may be present in an array, and find use in methods for evaluating methylation of CpG islands in cells. Kits and computer programming for use in practicing the subject methods are also provided.