The centrifugation vessel includes an outer wall containing an interior space. A dam defines a barrier which divides the interior space into at least two regions including a catch basin defining a higher gee region and a reservoir defining a lower gee region. These regions are joined together over the dam. The dam includes a face which is preferably tapered to enable optimization of speed of separation of a sample placed within the vessel. The vessel is usable in a biological sample processing method by having the higher gee region of the vessel configured to have an elongate form and the volume optimized for collection of a higher density fraction of the sample. Supply and withdrawal tubes extend into the regions for reliable extraction and separate collection of differing density fractions after separation by centrifugation.