There are numerous cooking oils on the market, each with their own virtues. One thing all oils have in common is that they will begin to smoke and break down if overheated. That temperature, called the smoke point, will vary from oil to oil depending on its source and how thoroughly it's refined. The best oils for high temperature cooking are those with the highest smoke points.
Measuring Smoke Points
There are several difficulties standing in the way of any authoritative, once-and-for-all guide to the smoke points of various oils. The climate and location the oil was produced in, its age, its purity and degree of refinement all play a part in when the oil begins to break down. Another thorny question is when the oil is considered to smoke: at the first wisp? At a given degree of visibility? In practice most vegetable oils, when fresh, can be used at temperatures well in excess of the normal frying temperature of 350 to 375 degrees.
High Temperature Oils
Several oils are well-suited for use at higher than normal frying temperatures. Grapeseed oil has a high smoke point and a neutral flavor, making it a good choice for most purposes. Peanut oil also performs well at high temperatures, though it does have a noticeable flavor and is a potential allergen. Sunflower, safflower, soybean and canola oil are all capable of high temperature cooking, though individual variability from bottle to bottle makes it difficult to say definitively which has the highest smoke point.
Special Cases: Butter and Olive Oil
Butter and olive oil are both cherished for their flavors, and both are generally considered unsuitable for high temperature use. Butter is a mediocre frying fat because it contains both water and milk solids, impurities that reduce its useful temperature. However, if the butter is melted and the water and solids are removed then the remaining, or clarified, butter can be used for high-temperature frying. Most olive oils can also be used for frying at higher temperatures, though their unique flavors are destroyed in the process. Olive oil remains a healthy choice, flavor notwithstanding.
Sheer high temperature performance is not the only factor to be considered in choosing a cooking oil. Avocado oil has a high smoke point, but its cost makes it impractical for day-to-day use. Many oils are partially hydrogenated to improve their shelf life, and these should be avoided. Read the labels and compare the levels of saturated fats, polyunsaturates and monounsaturates. Polyunsaturated fats are thought to help control cholesterol, while monounsaturated fats stabilize blood sugar. Some labels will also specify levels of Omega 3 and Omega 6 fatty acids, with Omega 3 being more desirable.