Different methods for the analysis of hazelnut oil and olive oil are compared in terms of the potential of each procedure in detecting compositional differences for evaluation of authenticity. These methods involve the use of different sample preparation techniques, namely simultaneous distillation−extraction (SDE) and supercritical fluid extraction (SFE), and the subsequent analysis by capillary gas chromatography using a programmable temperature vaporizer (PTV). On-line coupling of reversed-phase liquid chromatography to gas chromatography (RPLC−GC) was also considered for the analysis of the samples investigated. Working under the experimental conditions proposed, identification of olive oil, hazelnut oil, and mixtures of both oils (85:15) may be possible on the basis of the determination of the presence or absence of (E)-5-methylhept-2-en-4-one (filbertone). Keywords: Olive oil; hazelnut oil; filbertone; adulteration