It has been found that suitably light colored naphthenic acids can be produced from the crude acids by vacuum distillation to obtain a fraction free of impurities which apparently lead to color degradation. Also, it has been found that naphthenic acids may be contacted with formaldehyde or paraformaldehyde in the presence of sulfuric acid condensation catalyst to remove impurities in the form of a sludge which is separated by conventional means such as filtration, decantation and the like.