A subsea riser system comprising: a concentric subsea riser comprising an inner riser disposed within an outer riser and having an annulus between the inner riser and the outer riser; an upper riser assembly for connecting the subsea riser to a subsea buoyancy device (18, 19) and to a surface structure, the upper riser assembly comprising: a generally cylindrical member having a longitudinal bore, a lower end, an upper end, and an external generally cylindrical surface, the member comprising sufficient outtake ports (6A, 130) extending from the bore to the external generally cylindrical surface to accommodate flow of hydrocarbons from the subsea riser, and at least one port (6B, 158A) allowing flow of a functional fluid in the longitudinal bore, at least one of the outtake ports (6A, 130) fluidly connected to a production wing valve assembly for fluidly connecting the generally cylindrical member to the surface structure with a subsea flexible conduit, the upper end of the member comprising a connector suitable for connecting to a subsea buoyancy device (18, 19), and the lower end of the member comprising a profile suitable for fluidly connecting to the subsea riser; and a lower riser assembly for connecting the subsea riser to a seabed mooring and to a subsea hydrocarbon fluid source, the lower riser assembly comprising: a generally cylindrical member having a longitudinal bore, a lower end, an upper end, and an external generally cylindrical surface, the member comprising sufficient intake ports (8A/8B, 108A/108B) extending from the external surface to the bore to accommodate flow of hydrocarbons from the hydrocarbon fluid source as well as inflow of a functional fluid, at least one of the intake ports (8A/8B, 108A/108B) fluidly connected to a production wing valve assembly (114A/114B), the upper end of the member comprising a profile suitable for fluidly connecting to the subsea riser, and the lower end of the member comprising a connector suitable for connecting to a seabed mooring. a concentric subsea riser comprising an inner riser disposed within an outer riser and having an annulus between the inner riser and the outer riser; an upper riser assembly for connecting the subsea riser to a subsea buoyancy device (18, 19) and to a surface structure, the upper riser assembly comprising: a generally cylindrical member having a longitudinal bore, a lower end, an upper end, and an external generally cylindrical surface, the member comprising sufficient outtake ports (6A, 130) extending from the bore to the external generally cylindrical surface to accommodate flow of hydrocarbons from the subsea riser, and at least one port (6B, 158A) allowing flow of a functional fluid in the longitudinal bore, at least one of the outtake ports (6A, 130) fluidly connected to a production wing valve assembly for fluidly connecting the generally cylindrical member to the surface structure with a subsea flexible conduit, the upper end of the member comprising a connector suitable for connecting to a subsea buoyancy device (18, 19), and the lower end of the member comprising a profile suitable for fluidly connecting to the subsea riser; and a generally cylindrical member having a longitudinal bore, a lower end, an upper end, and an external generally cylindrical surface, the member comprising sufficient outtake ports (6A, 130) extending from the bore to the external generally cylindrical surface to accommodate flow of hydrocarbons from the subsea riser, and at least one port (6B, 158A) allowing flow of a functional fluid in the longitudinal bore, at least one of the outtake ports (6A, 130) fluidly connected to a production wing valve assembly for fluidly connecting the generally cylindrical member to the surface structure with a subsea flexible conduit, the upper end of the member comprising a connector suitable for connecting to a subsea buoyancy device (18, 19), and the lower end of the member comprising a profile suitable for fluidly connecting to the subsea riser; and a lower riser assembly for connecting the subsea riser to a seabed mooring and to a subsea hydrocarbon fluid source, the lower riser assembly comprising: a generally cylindrical member having a longitudinal bore, a lower end, an upper end, and an external generally cylindrical surface, the member comprising sufficient intake ports (8A/8B, 108A/108B) extending from the external surface to the bore to accommodate flow of hydrocarbons from the hydrocarbon fluid source as well as inflow of a functional fluid, at least one of the intake ports (8A/8B, 108A/108B) fluidly connected to a production wing valve assembly (114A/114B), the upper end of the member comprising a profile suitable for fluidly connecting to the subsea riser, and the lower end of the member comprising a connector suitable for connecting to a seabed mooring. a generally cylindrical member having a longitudinal bore, a lower end, an upper end, and an external generally cylindrical surface, the member comprising sufficient intake ports (8A/8B, 108A/108B) extending from the external surface to the bore to accommodate flow of hydrocarbons from the hydrocarbon fluid source as well as inflow of a functional fluid, at least one of the intake ports (8A/8B, 108A/108B) fluidly connected to a production wing valve assembly (114A/114B), the upper end of the member comprising a profile suitable for fluidly connecting to the subsea riser, and the lower end of the member comprising a connector suitable for connecting to a seabed mooring.