Select an oil. If you will be cooking Asian food, peanut or sesame oil might be ideal. Canola oil and olive oil work well for American and European cuisines, and grapeseed oil is both flavorful and healthful. Avoid expensive oils with subtle flavors, such as top-notch olive oil -- its subtleties will be drowned out by the chilies.
Add 1 cup of the oil to 2 to 3 tbsp. of chili paste into a glass jar. You may add more or less, to taste.
Stir the chili paste into the oil, with a spoon. Should the chili paste contain flakes that will not dissolve into the oil, place the oil and chili paste in a blender, and pulse until the texture of the mixture is uniform. Pour the oil mixture into the glass jar.
Add any additional ingredients to flavor your chili oil, such as star anise, scallions, onions or garlic. Cover the jar with a tight-fitting lid.
Allow your oil to steep for at least three hours -- or for days or months, depending on when you will be cooking and how strongly flavored you want it to be.