Longbow Research downgraded NewMarket Corporation to Neutral from Buy as volume growth failed to materialize and margins look stagnant.According to the analysts, petroleum additives volume declines being experienced by NewMarket appear to be company specific; they have no plausible rationale to believe the trend will reverse in 2H16.The company reported 2Q16 adjusted EPS of $5.50, beating Longbow's estimate of $5.43. "Expectations of higher additive prices in 2H16 along with the modest increase in base oil costs seen in 2Q16 suggest a more challenging margin environment for ASH and other lube producers," the analysts said.The analysts reduced their EPS estimates for 3Q16, 4Q16 to $5.35 (from $5.77) and $4.41 (from $4.88), respectively.