One of the mother french sauces, also know as the white sauce. It is basically a roux with a light stock added. This is a basis for a wide variety of sauces and dishes and is rarely used on it's own.
Combine flour and oil and cook for 2-3 minutes to form a pale roux. Add the stock slowly to the roux while whisking to avoid lumps. Simmer for approximately 45 minutes, skimming fat off the surface as needed.