Algae are among a number of organisms currently under investigation as sources of “single cell protein” for livestock or, less commonly, for human consumption. Other organisms being considered are various bacteria and fungi, including yeast, which can be cultured on a variety of substrates such a organic industrial wastes, and petroleum or fuel gas derivatives such as paraffin or methanol. Most of these alternatives involve culturing under industrial process conditions, using substrates which are subject to uncertainties in availability and fluctuations in cost. The current intensive level of research in this area is indicative of the growing market for non-conventional sources of protein. This major factors appear to be projected shortfalls in world protein production, and the diminishing cost barrier between non-conventional and conventional high protein sources.