NOVELTY - Selectively producing biofuel comprises: providing sealed reaction tank with lid (120), sampling and adjusting tube (140); providing conduit for passage of gas and stirrer; providing supply of algae and seed substance; providing temperature-control means; adding water (210), algae and seed substance to reaction tank to get liquid feedstock mixture; attaching lid to tank; using temperature control means to establish a temperature in reaction tank; activating stirrer to stir tank contents; obtaining sample of feedstock mixture; analyzing condition of the mixture; and collecting biofuel.    USE - The methods are useful for selectively producing a biofuel including methane, ethanol or biodiesel (claimed).    ADVANTAGE - The method: provides biofuel in more economically feasible manner by utilizing system requiring reduced space, and time for the production; provides biofuel in a single container, by regulating the internal biologically friendly environmental conditions; provides biofuel by utilizing self generated power i.e. true energy self sufficiency, in system; provides biofuel by utilizing system, which is simple and logical in construction; utilizes system operable even in remote areas by unskilled operator; and provides carbon dioxide which is traded for carbon credits.    DETAILED DESCRIPTION - Selectively producing a biofuel from algae, comprises: providing a sealed reaction tank with a lid (120), where the lid is removable and arranged to effect an airtight seal of the tank when installed on the tank; providing the tank with a sampling and adjusting tube (140) having two ends, an outer end and an inner end, where the tube extending downward into the tank so that the outer end is outside the tank and the inner end is inside the tank, the inner end being open, the outer end containing an airlock (141) for (a) allowing fluid to pass from the tank through the tube out through the airlock to permit sampling of the contents of the tank, and (b) preventing air from entering the container (100) via the airlock and the tube; providing at least one storage container; providing a conduit for passage of gas between the reaction tank and the storage container; providing a stirrer for stirring the contents of the tank; providing a supply of algae and a seed substance including bacteria or yeast; providing temperature-control means for the reaction tank; providing a source of water (210); adding a quantity of water, algae, and seed substance to the reaction tank to provide a liquid feedstock mixture in the tank; attaching the lid to the tank to seal the tank; using the temperature control means to establish a temperature within the reaction tank that is suitable for the bacteria or yeast to act on the liquid feedstock mixture to produce a biofuel including methane, ethanol or biodiesel; activating the stirrer to stir the contents of the tank; obtaining a sample of the feedstock mixture from the tank through the sampling and adjusting tube; analyzing at least one condition of the feedstock mixture obtained via the tube, where the condition includes chemical composition, nutrient level or pH, and if the condition is outside a predetermined tolerance range, then adjusting the composition of the feedstock mixture by adding a substance to the feedstock via the sampling and adjusting tube in order to maintain the condition of the feedstock within the predetermined tolerance range without allowing oxygen to enter the tank; and collecting the biofuel in the storage container, where the biofuel will be produced from the algae can be transferred to the storage container, and the feedstock mixture in the tank can be monitored and adjusted without admitting oxygen-containing ambient air into the tank. INDEPENDENT CLAIMS are also included for:    (1) producing biodiesel from algae, comprising: providing a reaction tank with a sealable and removable lid, and a mechanical stirrer with a motive source for actuating the stirrer; providing the tank with a sampling and adjusting tube having two ends, an outer end and an inner end; providing a supply of a naturally lipid and carbohydrate-containing algae; providing a supply of yeast; providing a temperature-control means for the reaction tank; providing a source of water; adding water, algae, and yeast to the reaction tank to provide a liquid feedstock mixture in the tank; using the temperature control means to establish a temperature within the reaction tank that is suitable for the yeast to cause fermentation of the algae in order to produce ethanol; stirring the mixture until the fermentation stops; sampling the mixture in the tank via the sampling and adjusting tube and analyzing the mixture to monitor the feedstock mixture in the tank; adding a base material to the mixture via the sampling and adjusting tube to cause transesterification of the mixture to produce biodiesel and glycerin; and allowing the biodiesel and glycerin to separate while at rest within the tank and removing the biodiesel from the reaction tank; and    (2) producing (P1) a biofuel including methane gas, ethanol or biodiesel, comprising: providing a reaction tank having a sealed lid; providing the tank with a sampling and adjusting tube having two ends, an outer end and an inner end; providing a storage container; providing a feedstock of algae in the tank; providing temperature control means for the tank; adding a seed material including bacteria or yeast to the tank to produce a feedstock material comprising the algae and the seed material; using the temperature control means to establish a predetermined temperature within the tank so that the seed material will cause the feedstock to ferment in order to produce a biofuel including methane, ethanol or biodiesel; monitoring the feedstock mixture in the tank by obtaining a sample of the feedstock mixture from the tank through the sampling and adjusting tube; and analyzing at least one condition of the feedstock mixture obtained via the sampling and adjusting tube, and thus produce a biofuel from algae and store the biofuel within the container and enabling the feedstock mixture in the tank to be monitored and adjusted without admitting oxygen-containing ambient air into the tank.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a system.    Container (100)    Lid (120)    Tube (140)    Airlock (141)    Water (210)