A fuel additive for a heavy fuel oil in composition form, the fuel additive comprising: 20 to 25% by weight of an oil soluble metallic compound; 30 to 35% by weight of an oxygen carrier; 15 to 20% by weight of a dispersant; 3 to 7% by weight of a lubricant; 8 to 15% by weight of a non-ionic surfactant; and 7 to 15% by weight of an overbased sulfonate-based a detergent, based on the total weight of the composition, wherein the oil soluble metallic compound is a calcium alkylbenzenesulfonate and the alkyl group has 8 to 50 carbon atoms, wherein the oxygen carrier is composed of at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diiosopropyl carbonate, dibutyl carbonate, dipentyl carbonate, methylethyl carbonate, methylpropyl carbonate and ethylpropyl carbonate, wherein the dispersant is a hydrotreated light distillate, wherein the lubricant is composed of at least one selected from the group consisting of a hydrotreated heavy paraffinic distillate, a hydrotreated light paraffinic distillate, a solvent-dewaxed heavy paraffinic distillate, a solvent-dewaxed light paraffin distillate, a hydrotreated and dewaxed heavy paraffinic distillate or a hydrotreated and dewaxed light paraffinic distillate, wherein the non-ionic surfactant is composed of at least one selected from the group consiting of sorbitan esters of fatty acids, polyetheyleneglycol esters of fatty acids and polyethyleneglycol sorbitan esters of fatty acids, wherein the overbased sulfonate-base detergent is composed of a compound of CAS Registration No. 68783-96-0 or a compound of CAS Registration No. 115733-10-3. 20 to 25% by weight of an oil soluble metallic compound; 30 to 35% by weight of an oxygen carrier; 15 to 20% by weight of a dispersant; 3 to 7% by weight of a lubricant; 8 to 15% by weight of a non-ionic surfactant; and 7 to 15% by weight of an overbased sulfonate-based a detergent, based on the total weight of the composition, wherein the oil soluble metallic compound is a calcium alkylbenzenesulfonate and the alkyl group has 8 to 50 carbon atoms, wherein the oxygen carrier is composed of at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diiosopropyl carbonate, dibutyl carbonate, dipentyl carbonate, methylethyl carbonate, methylpropyl carbonate and ethylpropyl carbonate, wherein the dispersant is a hydrotreated light distillate, wherein the lubricant is composed of at least one selected from the group consisting of a hydrotreated heavy paraffinic distillate, a hydrotreated light paraffinic distillate, a solvent-dewaxed heavy paraffinic distillate, a solvent-dewaxed light paraffin distillate, a hydrotreated and dewaxed heavy paraffinic distillate or a hydrotreated and dewaxed light paraffinic distillate, wherein the non-ionic surfactant is composed of at least one selected from the group consiting of sorbitan esters of fatty acids, polyetheyleneglycol esters of fatty acids and polyethyleneglycol sorbitan esters of fatty acids, wherein the overbased sulfonate-base detergent is composed of a compound of CAS Registration No. 68783-96-0 or a compound of CAS Registration No. 115733-10-3.