NOVELTY - Use of alkoxylated oligo- and polyamine (A) (having a number average molecular weight of 90-7000, and comprising 0.25-2 alkoxylate group of polyethylene imine structure (I) per nitrogen atom in the average for each molecule) for increasing the oxidation stability of organic liquids sensitive to oxidation, is claimed.    USE - The alkoxylated oligo- and polyamine is useful for increasing the oxidation stability of organic liquid sensitive to oxidation, where the liquid includes pure hydrocarbon, fuel, lubricant and fossils of plant or animal origin. The alkoxylated oligo- and polyamine is useful for increasing the oxidation stability of biofuel oils that are based on fatty acid esters or a mixture of biofuel oils having middle distillate (in an amount of 10-1000 wt. ppm, relative to the amount of biofuel oils) from fossil origin and/or plant and/or animal origin that essentially represents hydrocarbon mixture and free of fatty acid esters, and petrol (all claimed).    ADVANTAGE - The oligo- or polyamines act as highly effective antioxidants and are required only in less amount.    DETAILED DESCRIPTION - Use of alkoxylated oligo- and polyamine (A) (having a number average molecular weight of 90-7000, and comprising 0.25-2 alkoxylate group of polyethylene imine structure of formula (-(CxH2xO)p) (I) per nitrogen atom in the average for each molecule) for increasing the oxidation stability of organic liquids sensitive to oxidation, is claimed.    x = 2-6; and    p = 1-10.    INDEPENDENT CLAIMS are included for:    (1) a mixture from linear alkoxylated oligo- or polyamine (I) or crosslinked alkoxylated oligo- or polyamine having polyethylene imine structure of formula (-(CyH2yO)q) (II) (where the polyethylene imine backbone comprises a number average molecular weight of 300-5000), and biofuel oil based on fatty acid ester in a weight ratio of 1:100000 to 1:100;    (2) fuel comprising (a) a greater portion of a fuel oil, which comprises (i) 0.1-75 wt.% of at least one biofuel oil that is based on fatty acid esters, and (ii) 25-99.9 wt.% of middle distillate of fossil origin and/or plant and/or animal origin, which essentially represents hydrocarbon mixture and free of fatty acid esters, and (b) a lower portion of at least one linear or crosslinked oligo-or polyamine as above per se; and    (3) a stabilization formulation comprising (aa) 20-60 wt.% of one or more oligo- or polyamine as antioxidants, (bb) 10-30 wt.% of one or more conventional dispersants, (cc) 1-5 wt.% of one or more conventional metal deactivators, (dd) 0.01-0.5 wt.% of one or more conventional demulsifiers, and (ee) 4.5-68.99 wt.% of one or more conventional solvents.    y = 3 or 4; and    q = 1-3.