The key molecular-weight parameters of four different types of commercial fluorocarbon elastomers have been determined by size exclusion chromatography (SEC) for use in automotive alternative fuel applications. The number-, weight-, and z-average molecular weights (M(n)BAR, M(w)BAR, and M(z)BAR) obtained for the soluble fraction (98.5-100%) of each fluoroelastomer were compared with the Mooney viscosity provided by the suppliers. Correlations between the viscosity and any average molecular weight were generally poor. The best correlation coefficient found was naturally the value obtained between the viscosity and M(w)BAR. This paper also evaluates the molecular-weight degradation of some fluoroelastomeric materials during the compound processing. Even at relatively low shearing an accelerated rate of M(w)BAR degradation was observed in the early milling stages for a fluoroelastomer with longer-chain molecules (M(r) greater-than-or-equal-to 10(6)). The molecular-weight data provides in part a helpful insight in understanding the morphology of fluoroelastomer prototype parts which have been exposed to flexible fuel service conditions.