Stir-frying: how much of the oil evaporates? When you're stir-frying or sauteeing, I'm sure some of the oil get evaporated due to high temperature. How much of the original oil evaporates? Since I suppose it depends on the kind of oil, temperature and duration, can you give example for several typical cases? (for example, vegetable oil, medium heat, 15 minutes, etc)

How does this affect the nutrition and energy calculation? For example if 50 grams of vegetable oil contains ~400 kcal, how much calories does some food cooked with that much oil has?
The boiling point of most cooking oils is much higher than their smoke points.  The boiling point of olive oil, for example, is around 300°C (572°F), which is hotter than the temperature of a pan on a typical residential range/cooktop.  With that said, alcohols and esters which make up the flavor and fragrance of the oil will have lower boiling points and will therefore evaporate.  That should not significantly alter the nutritional content of the oil.  Furthermore, much of the perceived loss of oil is likely due to a combination of absorption of the oil into the items being fried, and also due to splatter.  The latter cannot be easily quantified due to its connection with the cooking vessel and the technique of the cook.