Although some privatization has been gradually done, there are still several state-owned companies of importance. The government keeps them as strategic assets or because they are natural monopoly. These include e.g. Neste (oil refining and marketing), VR (rail), Finnair, VTT (research) and Posti Group (mail). Depending on the strategic importance, the government may hold either 100%, 51% or less than 50% stock. Most of these have been transformed into regular limited companies, but some are quasi-governmental ("liikelaitos"), with debt backed by the state, as in the case of VTT.