The lipid classes and fatty acid profiles of oils extracted from male and female New Zealand Greenshell (Perna canaliculus) mussel samples either raw, or treated with heat or with high-pressure processing were compared. The Bligh and Dyer solvent extraction method was performed for mussel oil extraction. Iatroscan was used for lipid class determination, and gas chromatography—mass spectrometry was used for the fatty acid composition determination. Eight minutes of steaming time was required for the medium-size mussel meat placed as a single layer in a plastic pouch to achieve an internal temperature of at least 75°C. Female mussels had greater oil yield than male mussels on a dry weight basis, and female mussel oil extracts had a greater content of fatty acids than male mussels in general. No significant differences were observed in yield, lipid classes, and fatty acid compositions as a result of different treatments (raw, steamed, and high-pressure processing).