Nanoemulsion-based delivery systems are particularly effective tools for incorporating omega-3 polyunsaturated lipids into many foods and beverages. In this study, the impact of carrier oil type and concentration on the formation and stability of fish oil-in-water nanoemulsions was determined. Three carrier oils with different physicochemical and sensory properties were evaluated: medium chain triglycerides (MCT); lemon oil; and thyme oil. Nanoemulsions (d < 200 nm) were fabricated from oil phases containing lemon oil and MCT at all ratios with fish oil (0-100%), but only from thyme oil at high fish oil contents (75-100%). This effect was attributed to the high susceptibility of the nanoemulsions containing high levels of thyme oil to Ostwald ripening. Nanoemulsions fabricated from all carrier oils were physically stable (no increase in droplet size) during storage at 20 degrees C for 42 days when formulated from 75% fish oil and 25% carrier oil. However, carrier oil type did have an appreciable impact on the oxidative stability of these nanoemulsions, with the rate of lipid oxidation decreasing in the following order: MCT >> lemon oil > thyme oil. This effect was attributed to the presence of high levels of natural antioxidants (phenolics) within the lemon and thyme oils. These results show that selection of an appropriate carrier oil type and concentration can lead to the formation of fish oil nanoemulsions with good physical and chemical stability. (C) 2017 Elsevier Ltd. All rights reserved.