I was watching a discovery channel program the other day about the Canadian tar sands extraction work and they made a very good point. The sunken costs for the start up are the major expense and once that hurdle has been cleared the extraction process is relatively cheap. Of course, you've got to get someone to eat those start-up costs and the only entity likely to do that would be a government.
Traditionally oil companies form a consortium to spread the risk involved in exploiting a new field. Many overseas oil companies are essentially arms of their national governments, however.