Proximal composition, colour and levels of fatty acids and volatile compounds in oysters following high-pressure (HP) treatment at 260, 500 or 800 MPa for 3, 5 or 5 min, respectively, were investigated and compared to untreated oysters. HP-treated oysters had significantly (P<0.05) higher pH than untreated oysters. HP treatment also modified the gross composition of oyster tissue, the moisture content of HP-treated oyster being higher than that of untreated oyster. HP treatment at 260 MPa had less negative effects on oyster tissue colour (Hunter L-, a- and b-values) than treatment at higher pressures. HP treatment of oysters resulted in no significant changes in the fatty acid profile compared to untreated oysters. HP treatment of oysters, however, changed the level of volatile components when compared to the headspace of fresh oysters; HP-treated samples had higher concentrations of dimethyl sulfide, 1-penten-3-one, phenol and 1,2,4-trimethylbenzene relative to untreated samples. On the other hand, HP-treated oysters had lower concentrations of 1-penten-3-ol, 2,3-pentanedione, (EEZ)-1,3,5-octatriene and 1,3-octadiene than untreated samples. (C) 2007 Elsevier Ltd. All fights reserved.