What are the differences between fentanyl patches and oxycontin?

Half-life & delivery. Both are opioids but stay in your body for different lengths of time (half-life) and, of course differ in their delivery (oral versus patch).
Both narcotics. Fentanyl and Oxycontin are both narcotics. Fentanyl is normally an intravenous medication when formulated as a skin patch it delivers a constant dose of medication over time. Usually giving pain relief upto 72 hrs. This formulation is usually reserved for patients who are narcotic tolerant. Oxycontin is an oral preparation and is given every 12 hours and bus indicated for acute pain.