Twenty-three muskoxen (Ovibos moschatus) housed in a captive facility for rewilding in Sweden were chemically immobilized for annual health evaluations and hoof trimming. The muskoxen were darted in May to September (2012–15) in their holding pen with etorphine (0.015 mg/kg) and xylazine (0.1 mg/kg) intramuscularly. Twenty-two of the 23 animals were immobilized with a single dart injection. The mean (SD) induction time was 4 (2) min. Arterial blood gases were collected from 18 animals. All animals were severely hypoxemic with varying degrees of respiratory acidosis. The hypoxemia resolved in 17 of 18 animals with intranasal oxygen supplementation at 1 L/min per 100 kg. Relative arterial oxygen saturation (SpO₂) measured by pulse oximetry was significantly higher than the arterial oxygen saturation calculated from the partial pressure of arterial oxygen (SaO₂) obtained by a blood gas analyzer. Based on these findings, muskox can be immobilized successfully with etorphine (0.015 mg/kg) and xylazine (0.1 mg/kg) but should receive supplemental oxygen.