A method is provided to produce biodiesel from algae using a strain of microalga chlorella protothecoids, by screening a specific strain with characteristics of high yield of biomass and high oil content, cultivating the screened strain for high-cell-density growth for up to 108 grams of dry cell weight per liter of the suspension in a bioreactor using solutions containing carbohydrates as feed, harvesting and drying the high density cultivated algal cells to extract oil from the dried algal cells, and producing the biodiesel by reaction of catalyzed transesterification using the extracted oil as feedstock.