A solvent blend for breaking down and reducing the viscosity of petroleum substance consists essentially of one or more methyl esters of C14-C18 fatty acids, one or more C9-C20 low aromatic hydrocarbon solvents, and one or more C4-C8 high aromatic hydrocarbon solvents, with the high aromatic solvent fraction being dispersed within the solvent blend in droplet form. The solvent blend may be produced by mixing the high aromatic solvent fraction into an intermediate or base blend consisting essentially of the methyl ester fraction and the low aromatic solvent fraction, with the base blend being produced by mixing the lower aromatic solvent fraction into the methyl ester fraction such that the lower aromatic solvent fraction is dispersed within the methyl ester fraction in droplet form.