There is no ceiling dose when it comes to oxycodone. As long as you have the tolerance to hence "tolerate" a certain dose of an opiate, you can tolerate it. Tolerance does build faster to the euphoric effects of opiates than some of the other effects like respiratory depression, but opiate users usually have a pretty good idea on what they can handle and know that the opiate "magic" does fade to a degree regardless of dose or ROA. To answer Beefy's question, there is definite cross-tolerance between opioids, however a new opioid will render a different feeling even at an equipotent dose, and starting off with a somewhat lower dose than what is equipotent is wise. So, yes if you have a high tolerance to heroin and methadone, you have general opioid tolerance, but not specific to oxycodone since you haven't used it in particular. These questions aren't cut and dry, tolerance is a tricky thing.
