The oxygen production rates for a cyanobacterial suspension flowing in straight and coiled tubes were measured to find a way of achieving higher efficiency of light utilization by means of convective mixing. The photosynthetic flow chambers were made of glass tubes and illumination was by fluorescent light. The cyanobacterium used was Spirulina platensis, which has a high growth rate. The oxygen production rate for fluid flow in straight and coiled tubes increase with the increase in Reynolds number. The maximum oxygen production rate was achieved at 30°C for both tube reactors, but the oxygen production rate was higher for the coiled tube unit than the straight tube unit at 30°C. Thus the convective mixing generated in the coiled tube reactor contributed to an increased in light utilization, which played an important part in improving the oxygen production rate.