What phoneme symbols does Google show in its search results?

I did some investigation and I have determined that the dictionary entries returned by the Google define: operator are from the New Oxford American Dictionary, including the pronunciation symbols. The OxfordDictionaries.com site has a complete key to these pronunciations.

To determine this, I started the Wikipedia article that compares many of these "pronunciation respelling" systems, and looked up the various example words to see which system on that page most closely matched the system used by the Google dictionary search results. The only scheme that matched perfectly is the one labeled NOAD, for New Oxford American Dictionary.

Furthermore, once I made this determination, I was reminded that the Dictionary app which comes with Mac OS X also gets its data from the New Oxford American Dictionary, and I found that this was indeed the case—the definition content matches exactly.

However, the Wikipedia article on Google Dictionary reports that the content is from Oxford American College Dictionary. In any case, it appears that the content, including pronunciations, comes from the American English department of Oxford Dictionaries.