A method of manufacturing a fibrous, oxygen barrier film comprising the steps of: - providing a suspension comprising: i. a first microfibrillated cellulose in an amount of at least 50 weight %, wherein said first MFC exhibits an SR value of at least 85, ii. reinforcement fibers, having a weighted fiber length of >0,8 mm and an SR value of below 50, in an amount of at least 5 weight %, iii. a formation aid chosen from the group consisting of anionic polyelectrolytes, a second finer MFC having an SR value higher than that of the first MFC, modified starch, gum-like natural polymers or their synthetic equivalents, polyethylene oxides, metaphosphates and unmodified or modified PVA, in an amount sufficient for generating a specific formation number below 0.45 g 0.5 /m in the fibrous oxygen barrier film, all percentages calculated on the total solid content of said suspension, - mixing said suspension to form a mixture, - forming a fibrous web from said mixture, - dewatering and/or drying said fibrous web to form a film having a basis weight of less than 40 g/m 2, a specific formation number of below 0.45 g 0.5 /m, and an Oxygen Transmission Rate value of below 100 ml/m 2 /per 24h at 50% RH determined at 50% relative humidity in accordance with ASTM D 3985-05. - providing a suspension comprising: i. a first microfibrillated cellulose in an amount of at least 50 weight %, wherein said first MFC exhibits an SR value of at least 85, ii. reinforcement fibers, having a weighted fiber length of >0,8 mm and an SR value of below 50, in an amount of at least 5 weight %, iii. a formation aid chosen from the group consisting of anionic polyelectrolytes, a second finer MFC having an SR value higher than that of the first MFC, modified starch, gum-like natural polymers or their synthetic equivalents, polyethylene oxides, metaphosphates and unmodified or modified PVA, in an amount sufficient for generating a specific formation number below 0.45 g 0.5 /m in the fibrous oxygen barrier film, all percentages calculated on the total solid content of said suspension, i. a first microfibrillated cellulose in an amount of at least 50 weight %, wherein said first MFC exhibits an SR value of at least 85, ii. reinforcement fibers, having a weighted fiber length of >0,8 mm and an SR value of below 50, in an amount of at least 5 weight %, iii. a formation aid chosen from the group consisting of anionic polyelectrolytes, a second finer MFC having an SR value higher than that of the first MFC, modified starch, gum-like natural polymers or their synthetic equivalents, polyethylene oxides, metaphosphates and unmodified or modified PVA, in an amount sufficient for generating a specific formation number below 0.45 g 0.5 /m in the fibrous oxygen barrier film, all percentages calculated on the total solid content of said suspension, - mixing said suspension to form a mixture, - forming a fibrous web from said mixture, - dewatering and/or drying said fibrous web to form a film having a basis weight of less than 40 g/m 2, a specific formation number of below 0.45 g 0.5 /m, and an Oxygen Transmission Rate value of below 100 ml/m 2 /per 24h at 50% RH determined at 50% relative humidity in accordance with ASTM D 3985-05.