Dr. O'Neill is an Adjunct Professor of Surgery and Medicine and the Medical Director for the Division of Undersea & Hyperbaric Medicine (UHM) at Phelps Hospital Northwell Health. Dr. O'Neill provides both clinical and research services in Undersea & Hyperbaric for the Westchester Community for almost 3 decades, providing treatments in the largest hyperbaric chamber program in the Northeastern United States. He specializes in patients with diabetic and surgical wounds, adverse effects of radiation therapy, sudden sensorineural hearing loss, carbon monoxide poisoning, decompression sickness, and a variety of other complex medical and surgical diagnoses. He is the principle investigator of a number of undersea & hyperbaric studies both ongoing and published, from preventing adverse effects of clinical hyperbaric oxygen treatment, to the health maintenance of commercial scuba divers and compressed air workers. Dr. O'Neill is a leading authority in both diving and hyperbaric medicine and serves on the Board of Directors of the Undersea & Hyperbaric Medical Society (UHMS), and is Co-Chairman of the Education Committee, Publications and Diving Committees. Dr. O'Neill earned his bachelor's degree with distinction from Iona College and his medical degree from the Universidad Central del Este. He completed residency training in general surgery and internal medicine at Montefiore New Rochelle, and a research fellowship in Burn Surgery at New York Medical College, University Hospital. He completed Undersea & Hyperbaric Medicine training with Dr. Eric Kindwall in the National Certification program in UHM , University of Wisconsin. He also earned a Master of Public Health degree from the Johns Hopkins University, Bloomberg School of Public Health, with concentrations in Occupational Health and Environmental Engineering.