NOVELTY - Cultivation method (M1) of microalgae involves culturing microalgae capable of forming biofilm on surface of liquid to obtain biofilm formed on liquid surface of liquid culture medium.    USE - The method (M1) is useful for cultivation of microalgae used for obtaining biofilm, which is used for obtaining oil, biomass and biomass fuel (all claimed).    ADVANTAGE - The cultivation method significantly reduces production cost of microalgae-derived biomass. The method enables improved and high recovery of the microalgae from the culture medium in a very easy manner when compared to existing cell suspension culturing methodologies, as cultured microalgae floats on the culture medium. As the biofilm is collected from the culture medium it is not required to recover the microalgae from the culture medium and only the moisture content contained in the biofilm on the surface of the liquid is collected, hence cost of collection is also significantly reduced. The method does not have the need to handle several liquid media and water. The production cost of the biomass is also significantly reduced. The microalgae enable efficient collection of the biofilm and drying of the biomass for efficient extraction of oil from the biomass. The effective collection of the microalgal biomass prevents global warming.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) biofilm (BF1) formed on surface of the liquid level obtained by the above-mentioned cultivation method;    (2) microalgae capable of forming biofilm on the surface of the liquid;    (3) biofilm (BF2) formed on the liquid level of the above-mentioned microalgae;    (4) biomass obtained from the above-mentioned biofilm;    (5) oil obtained from the above-mentioned biofilm;    (6) method (M2) for collecting the biofilm, involves collecting the biofilm by depositing or transferring the biofilm formed on the liquid level on to substrate; and    (7) method for preparing biomass fuel using the above-mentioned biofilm as a fuel.