A dielectric fluid composition for electrical apparatus comprises a functionalized 12-hydroxy stearic acid having desirable properties including a pour point less than −30° C. and a fire point greater than 250° C. It may be prepared by a process wherein 12-hydroxy methyl stearate is transesterified by reaction with a C3-C20 alcohol to form an alkyl-12-hydroxy stearate, followed by esterification thereof with a linear or branched C4-C20 carboxylic acid. This acid may be a free acid chloride, a fatty acid, a carboxylic acid anhydride, or combination thereof. The resulting functionalized 12-hydroxy stearic acid exhibits improved thermoxidative capability, low temperature flowability, and increased fire point.