We compared the actual oxygen concentration reaching the airway of 10 patients with the preset oxygen concentration delivered from single and double jet nebulizers to face tents. We measured hypopharyngeal oxygen concentration (FHO2), which closely approximates tracheal fractional inspired oxygen concentration (FIO2), using the Nasal Oxygen Sampler we have previously described. All nebulizers were powered by 12-14 L/min of 100% oxygen, and nebulizer settings were varied between 40% and 100% oxygen. The FHO2 never closely approximated the oxygen concentrations delivered from the nebulizer to the face tent. There was no significant difference in FHO2 between single- and double-nebulizer systems.