Sources of finance - raising £12bn from sale of assets

The textbooks like to use the concept of a “sale of assets” as a means by which a firm can raise finance. They usually mention things like factory machinery and motor vehicles, or perhaps some spare land & buildings. But I bet they never thought of the likes of BP - which aims to raise £12bn from an asset sale to finance the costs of the Gulf oil spill. The “assets” concerned include existing oil wells where extraction has already commenced, as well as the “rights” to drill in certain oil fields - a good example of an intangible asset which is being sold to raise cash.