Optical density, chlorophyll, carotenoids and oil contents were the highest at 10 mM malonate; higher concentrations were inhibitory (with few exceptions). Rates of respiratory oxygen uptake also decreased at malonate concentrations above 10 mM. Dry mass was, however, continually increasing by increased malonate concentrations. Free glycerol contents have not been generally altered by malonate concentrations, with few exceptions. The above-mentioned observations were consistent at all of the studied species (local isolates of Chlorococcum humicola, Scenedesmus dimorphus, Scenedesmus acutiformis and Scenedesmus quadricauda), except in the dry mass of Chlamydomonas (SAG isolate (Samlung für Algen kulturen). The inhibitory action on respiration by malonate concentration above 10 mM was accompanied by lipoid decrease. Thus, the hypothesis of competitive inhibition of succinate dehydrogenase (SD) by malonate, with increased acetyl CoA and subsequently triglycerides, is ruled out at malonate concentration above 10 mM. Increased oil yield at ≤ 10 mM malonate resulted from increased culture cell density along with increased oil content per cell. Doubling oil and dry mass contents in one litre (10 mM) of the studied algae roughly costs 0.23€.