Microalgal cultures represent a promising alternative source of biomass for biofuel and chemicals production, since they can reach higher energy yields per area than conventional biomass crops and can be grown on marginal land using waste, saline or brackish water. Their use can thus avoid the food-fuel competition for land, resulting in major economic and social benefits. At the present stage however, major developments are needed for making microalgae-to-biofuels process technologically and economically feasible. With respect to a sustainable microalgal biomass production, the following parameters are thought to be of utmost importance: CO2 concentration; light intensity and quality, photoperiod; photobioreactor design; batch, fed-batch or continuous conditions; possible use of wastewater streams. The purpose of the ongoing research is thus to clearly assess the potential and real influence of these parameters on the quantitative and qualitative production of biomass, lipids and added-value chemicals by several microalgal species; and on their respective productivity, taking into account the probable antagonism between biomass and lipid production, often depending on the nitrogen supply. Several species of microalgae are grown at laboratory scale to compare and contrast biomass yield and lipid productivity. In addition to the potential use of oil for biodiesel production, we are currently working towards demonstrating the technical and economical feasibility of an innovative process for syngas production by hydrothermal processing of microalgae. The process is envisioned as a closed-cycle with respects to nutrients, water and CO2, that are separated and reused for microalgae growth, potentially resulting in a sustainable process.