Abstract: A bioreactor for biomass production having (i) a substantially transparent chamber, the chamber being suitable for containing biomass in a liquid phase, and having a base portion, an upper portion and a number of sidewalls between the base portion and the upper portion, the sidewalls being configured so as to diverge from the base portion towards the upper portion; and (ii) a circulating means for circulating the contents of the chamber to create a motive force in the liquid phase to ensure continual mixing of all of the biomass and a semi-continuous exposure of the biomass to a light source.