A fluid flow control system serving as an inflow port from a fluid reservoir (R) to the interior of a production pipe (S) is in the form of a housing (3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j, 3k, 31). The housing has a primary flow path (18) and a secondary flow path (19). The secondary flow path is in fluid communication with a chamber (B) in which is arranged an actuator (5) for a valve device (4), the valve device arranged to open and close the primary flow path. At least one flow restrictor (1,2) is arranged in the secondary flow path, the flow restrictor arranged to provide a pressure to chamber (B) sufficient to actuate the valve to an open position when the fluid flowing through the secondary flow path is oil, and a pressure sufficient to actuate the valve to a closed position when the fluid has a viscosity and/or density less than oil.