Disclosed is a riser including a plurality of pipelines. In one example there are three such pipelines extending from the seabed toward the surface and having an upper end supported at a depth below the sea surface. In one embodiment, a first of the pipelines acts as a central structural core, and the other pipelines are arranged around the first pipeline. In another embodiment, three pipelines are arranged around a structural core. In each case, the first of the pipelines can be a fluid injection line, and the other pipelines are production lines. Also disclosed is a riser having buoyancy along at least a part of its length. The buoyancy results in the riser having a generally circular cross-section, the circumference of which is non-contiguous. Methods of installing such risers are also described.