Optimal formulations of low-viscosity marine fuel (LMF) involving heavy diesel fractions of secondary origin and containing cold flow improvers and antioxidants have been found by mathematical modeling using the pour point, sulfur content, and density as critical parameters. The experimentally obtained characteristics of laboratory LMF samples prepared according to the calculated formulations correlate well with theoretical data and comply with the requirements of regulatory documents. The possibility of involving heavy distillates, produced by Angarsk Petrochemical Company, in LMF is shown. The antioxidant Kerobit TP 26 P is proposed as a stabilizer in the production of LMF composed of a heavier diesel fraction from the atmospheric column of the GK-3 unit and the atmospheric-vacuum distillation residue of the hydrogenated product from units for hydrotreating of heavy middle-distillate fractions of primary and secondary oil refining. The effectiveness of the antioxidant has been evaluated in terms of change in total sediment, which is a measure of oxidative stability, as well as by the existent gum content. The EPR technique has proved the occurrence of radical reactions during storage of heavy diesel fractions of secondary origin and the inhibitory effect of Kerobit-TP 26 P on these processes.