Abstract: An open, continuous system for culturing Chaetoceros sp. microalgae includes a large outdoor container and full strength sunlight as a light source. The container is preferably a fiberglass tank having an open top, a diameter of approximately 18 inches, and a height of about 5 feet. The container holds a culture medium having the following characteristics: a carbon dioxide controlled pH of about 8.2, a starting nitrogen concentration of at least 3.0 mg N/liter, a starting phosphorous concentration of at least 2.75 mg P/liter, a starting vitamin B12 concentration of at least 5 micrograms/liter, a starting iron chloride concentration of at least 0.3 mg/liter, a starting copper sulfate concentration of at least 0.01 mg/liter, a starting silicate concentration of at least 10 mg SiO2/liter, and a Na2EDTA concentration of 5 mg/liter. The medium is inoculated with a seed stock of Chaetoceros sp. microalgae and exposed direct sunlight.