Personnel who operate the drilling rig. The crew typically consists of roustabouts, roughnecks, floor hands, lead tong operators, motormen, derrickmen, assistant drillers, and the driller. Since drilling rigs operate around the clock, there are at least two crews (twelve hour work shifts called tours, more common when operating offshore), or three crews (eight hour tours, more common onshore). In addition, drilling contractors must be able to supply relief crews from time to time when crew members are unavailable. Though less common now than in years past, the drilling contractor may opt to hire only a driller, and the driller in turn is responsible for hiring everyone reporting to him.