Although adaptation to shiftwork has been widely studied, little is known about how individual and environmental factors combine to influence sleep among shiftworkers. This study examined age, smoking, and negative affectivity (NA) as predictors of sleep duration and quality for 3 work phases (day shifts, DS; night shifts, NS; and leave periods, LP). Data were collected from personnel working 12-hr shifts, onshore (n = 330) or offshore (n = 456). Individual factors predicted patterns of sleep measures across the DS, NS, and LP phases onshore, but not offshore; onshore, work phase interacted with smoking and with age to predict sleep duration and with NA to predict sleep quality. The role of the offshore environment in shiftwork adaptation is discussed.