Principal formulation effects on oil-fluoroelastomer compatibility in European specification tests are reviewed, and detailed surface analysis of elastomer samples after exposure to oil reported. The mechanism of fluoroelastomer degradation has been investigated and found to be based on fluorine depletion of a thin surface layer by dispersant additives. Compatibility is determined by both the oil and the detailed composition of the elastomer. Correlations with field performance have not been published for current European elastomer tests. Failing oils have demonstrated satisfactory performance in field trials. Oil preageing affects seal compatibility, but probably differently for gasoline and diesel engine lubricants.