A method and system are provided for supporting the growth of algae cells. In the method, an inoculum of algae cells are grown in a closed bioreactor. Thereafter, the inoculum of algae cells is passed into an open system. Specifically, the inoculum is passed into an expanding plug flow reactor (EPFR) having an increasing width from its first to its second end. Further, medium is introduced into the EPFR to maintain a selected shallow depth. Importantly, the medium provides sufficient nutrients to support logarithmic growth of the algae cells to maintain a high concentration of algae cells, i.e., at least 0.5 grams per liter of medium, in the EPFR. After the desired level of growth is reached, the algae cells are transferred to a standard plug flow reactor wherein oil production is activated in the algae cells.
