in this case the subcritical steam is usually injected into a well arrangement via an injector well this is described in more detail below the methods of the present invention are carried out in an apparatus comprising i an inlet for water ii a supercritical steam boiler connected to said inlet for producing supercritical steam iii an expansion unit connected to said supercritical steam boiler for converting said supercritical steam to subcritical steam and iv an outlet connected to said expansion unit for delivery of said supercritical steam to said system a preferred apparatus further comprises a separator in between the expansion unit and the outlet for separating steam and water and or impurities so that the subcritical steam passes through the separator before it is delivered to the system preferably an inlet of the separator is connected to an outlet of the expansion unit preferably an outlet of the separator is connected to the apparatus outlet for delivery of steam the inclusion of a separator is advantageous because it means that if supercritical steam is converted to subcritical steam comprising a steam and water mixture as described above that the water can easily be removed along with impurities preferably therefore the separator further comprises a water outlet still more preferably this water outlet is connected to a water purifier the quality of steam injected to the hydrocarbon system tends to be higher when such a separator is present as described above the methods of the present invention may be combined with a conventional i e non.