The relationship of engine test sludge to field sludge was investigated by a variety of analytical techniques. Engine oil drains and sludges are suspensions of aggregated, resinous particles in oil. The sludges, in particular, contain large particle networks which are readily broken under shear. The resinous phase itself contains highly oxidized fuel fragments, and is enriched in aromatics, acidic species, and additive elements relative to the hulk oil. Field sludge and drain oil samples from the U.S., Europe, and the Far East are shown to be chemically similar to sequence VE engine test sludge and drain oil. Fleet test drain oils from vehicles powered by the Daimler Bens M102E engine are shown to be chemically similar to M102E engine test drain oils. The VE test is different from the M102E test: the VE engine test emphasizes the build-up of nitro-oxidized fuel fragments in the drain oils, compared to the M102E test which emphasizes the build-up of fuel residue in the drain oils.