This study will enroll individuals with ARDS at four Baltimore hospitals. Participants will be randomly assigned to receive either HFOV-Hi or HFOV-Lo. All participants will receive their assigned HFOV method for 7 days, until spontaneous breathing occurs, or until death, whichever occurs first. Blood collected at baseline and Days 1 and 3 will be analyzed for markers of inflammation and lung injury. Participants' clinical status will be monitored until they no longer need ventilation and return home, or for up to 60 days while in the hospital. Individuals being treated for ARDS at the participating hospitals who decline to enroll in the study will be asked for permission to monitor their medical progress. These individuals will not take part in any study procedures, but their clinical information will be used for comparison purposes. Additionally, clinical information on other ARDS patients admitted to the hospital over the previous 2 years will be analyzed.