Supposively when you shoot it, Opana is at least 10 times stronger than oxycodone milli for milli. I've seen figures like 1mg Opana (oxymorphone) = 20mg oxycodone when IV'd, as well. There is a big jump for snorting...intranasally, I've seen people report that 1mg of opana = around 5mg oxy...but realistically opana is about twice as strong as oxy (unless you've been doing other opiates and then do opana for the first time, of course its going to feel stronger). Truth be told, even the more reliable conversion charts are only accurate when there are no opiates in the user's system. Just be extra careful if you're used to taking or snorting opana, because it is way more intense when injected - like Dilaudid.
edit: I could be wrong in my figures about IV opana so please correct me, only going on what I've read.