Abstract: A method of controlling flows from plural hydrocarbon extraction wellhead trees (50, 52, 54, 56) in an extraction system including plural wellhead trees (50) connected by a pipeline network (60, 62, 88, 104) to a host facility (64) via a manifold system (130, 132) situated remotely from the host facility (64). Each wellhead tree (50) has a production outlet connected by a production conduit (88) to the manifold system (130, 132) and a test flow outlet (76) connected by a test conduit (104) to the manifold system (130, 132). Wellhead tree outlet valves are operable to divert the flow from one wellhead tree only to the manifold system (130, 132) from where it is routed via a test pipeline (62) to testing equipment at the host facility. Alternatively, one or more modules (132) of the manifold system (130, 132) may be replaced by one or more different modules each containing a multi-phase flow meter so that testing can take place at the manifold system.