Undiluted, commercial orange oils were exposed to oxygen and stored in darkness for up to three months at room temperature to compare their relative oxidative stability. Sensory evaluations indicated that in essence oil, EO, aroma had been altered more than in the cold pressed oil, CPO, characterised primarily by the loss of citrus character rather than pronounced off-flavours. MS analyses indicated increased levels of terpene oxides and ketones, but greatly reduced levels of terpene aldehydes. Major increases of limonene oxides (8 to 9 fold) and cis and trans p-2,8-menthadiene-1-ol (3 to 4 fold) were observed in both oil types, but initial and final levels were always higher in EO. Common acid catalysed hydration products of limonene such as terpene-4-ol, and α-terpineol decreased approximately 10% in both types during storage. Decanal and octanal decreased 37% and 38% respectively in EO, whereas only 26-27% was lost in CPO. Losses of citronellal, dodecanal and β-sinsensal ranged from 52 to 63% in EO but only 27 to 31% in CPO. Putative off-flavour compounds such as carvone and carveol increased 3 to 6 fold during storage but were always twice as high in EO. Time-intensity GCO confirmed the loss of critical aldehydes, but also demonstrated that the aroma impact of produced carveol and carvone were minimal. Observed sensory changes were due to losses of potent aldehydes and ketones. The total carotenoid concentration in the CP oil decreased by 54% during 12 weeks storage suggesting that they may act as sacrificial antioxidants. © 2006 Elsevier B.V. All rights reserved.