A device for reducing friction of a viscous fluid flow in a conduit is disclosed. The device comprises a body positionable to define at least a segment of a flow path for the viscous fluid in or contiguous with the conduit, a cavity in the body for retaining lubricating fluid, and at least one port in the body for delivering lubricating fluid to the cavity. A fluid outlet arrangement from said cavity delivers lubricating fluid to the flow path to form a downstream lubricating film at the conduit surface. The fluid outlet arrangement comprises a substantially continuous opening or ring of close spaced openings, effective collectively to reduce the pressure variation and therefore velocity variation of the delivered lubricating fluid along said outlet arrangement.