Twenty patients undergoing outpatient facial plastic surgery with local anesthesia and intravenous sedation were prospectively studied. The specific aims were to (1) estimate the oxygen concentration in different locations around the face and (2) compare the amount of oxygen escape in the surroundings, using either a nasal cannula or a posterior pharyngeal catheter. The project was carried out in two parts. Each subject was supine, and oxygen supplementation at 3 liters per minute was applied by nasal cannula. The oxygen concentration of twenty-four different set locations around the patient's face was analyzed using the Random Access Mass Spectrometer (RAMS) unit, starting at the right and left lateral alar rim and 2 cm intervals laterally, superiorly and inferiorly. The procedure was repeated using a posterior pharyngeal catheter with the oxygen cannula fed down the red-rubber catheter. Statistical analysis has showed that in all sites at or above the nasal area, the difference between the nasal cannula and posterior pharyngeal catheter is significantly greater than 0, indicating that higher concentrations are observed with the nasal cannula than with the posterior pharyngeal catheter (p=0.004).