group IV oil

Does anyone know where to find a list of what constitutes a group IV base stock?(other than PAO) I called Shell and asked them and they told me that they would not label Rotella T Synthetic as a synthetic unless it had a group IV base stock, but didn't have anymore info than that. The inference being that RTS is a group IV oil and not a group III as is so often stated on several different boards. Any leads to find a complete list of group IV base stocks, would be most appreciated. Steve