Robot Overlord said:
Only by virtue of dosage, not a difference in chemical strengths.
Percocet / Percodan (and generics) = Acetaminophen or Asprin (respectively) and Oxycodone (usually 5mg).
Oxycontin = Oxycodone in 20mgs, 40mgs and 80mgs in regular or time-release coated pills.
Body metabolizes Oxycodone and converts it to morphine at a ratio of 1.75mg Oxy : 1mg Morphine
Pure Heroin (medically Diamorphine) has a ratio of 2 : 1
Hydromorphone (sold as Dilaudid, or generically "Hydromorph Contin") is 5 : 1 ...
The all opiates and opioids can be interpreted in terms of standardized chemical and dosage strength as (SUBSTANCE)mg : 1mg Morphine, as indexed.
I *believe* Hydromorphone is the 2nd strongest opioid, with a rather yawning gap between the 1st place heavyweight being Fentanyl (marketed as Sublimaze), which has a strength of 100 : 1 and, because of it's extreme potency is almost exclusively administered through trans-dermal skin patches. Attempts at directly ingesting Fentanyl by opiate addicts have resulted in a lot of accidental ODs.
Also, while Opiate is a catch all term for any medicine or drug that breaks down into morphine when introduced to the human system (including morphine, itself), "Opiates" is a term technically associated exclusively with drugs and chemicals synthesized with the naturally occuring alkaloids in opium poppy resin. "Opioids" are functionally identical to Opiates, but describe a class of drugs that are synthesized without using any naturally occuring ingredients - Oxycodone, Hydromorphone and Fentanyl are all Opioids.
... Just... you know, to expand on your statement... Pretty sure I've got my facts straight, but I'm just an interested layman speaking from memory, so don't take it as red w/o research...
TL;DR
Percocet and Oxycontin share the same active ingredient. Percocet just has less of it and also has some OTC stuff.