Abstract: Downhole apparatus for separation of oil from oily water or water from oil having an internal chamber continuously flooded with production fluids from a well, one or more hydrocyclonic separators for separating the production fluid into a stream enriched in oil and an stream depleted in oil. The clearance required between the apparatus and the well casing being the minimum required for running the apparatus into the casing, maximizing the size of the separator(s) and improving capacity. A range of artificial lift devices is included to bring the oil enriched stream to the surface if the natural pressure of the reservoir is insufficient. Substantial axial overlap of multiple separators is provided for better compactness and capacity of the apparatus. Pipes from separator overflow outlets connect to a common overflow manifold, and pipes from the separator underflow outlets connect to a common underflow manifold.