Participants in this observational study will take part in multiple trials in which they have the opportunity to choose either HYD or money. On the first two experimental days, prior to choice sessions, participants will receive a sample of the drug doses that can be chosen. During test sessions, participants will have 12 opportunities to choose either drug or money. Participants will use a computer to earn choices. Respiration rate, oxygen saturation, heart rate, and blood pressure will be monitored throughout choice trials. Supplemental HYD will be made available following some choice sessions. Self-report questionnaires will be completed at different times during the study. Participants will be maintained on buprenorphine throughout the study, with a minimum 2-week lead before the experiment, and a fixed 3-week detoxification after study completion.