Q: What liquid is compatible to mix with scented oils and will not separate, but blend?
A: First, I assume that by "scented oils" that you mean essential oils like Cypress and Lavender and not synthetic fragrance oils. We don't deal in synthetics in any way and do not recommend them. So, the answer is that all essential oils can be mixed (diluted) into any carrier oil.
Carrier oils are oils like Sweet Almond, Grapeseed, Olive, Safflower, etc. For most aromatherapy blends, the ratio is approximately 2 drops of essential oil to 1 teaspoon of carrier oil. Essential oils will also mix with alcohol but this is generally not done. Essential oils will not mix with water without other additives.
To learn more about blending essential oils + recipes for essential oil blends, click here.