A soot reduction additive for use in the in-situ burning of oil spills has been developed. The additive is in the form of a liquid concentrate that can be sprayed on a spill. The soot producing tendency of hydrocarbons decreases in the order: aromatics, branched paraffins, cycloalkanes, normal paraffins. Similarly, the soot reduction ability of ferrocene and derivatives decreases in the order: aromatics, cycloalkanes, branched paraffins, normal paraffins. A method of predicting soot reduction is inferred from model studies and confirmation obtained from experiments on known hydrocarbon mixtures.