A method for recovering oil (24) from a natural oil reservoir (18) includes the steps of separating air to produce an oxygen rich stream (40) and a nitrogen rich stream (34), providing a natural gas stream (12) and feeding at least part of the oxygen rich stream (40) and the natural gas stream (12) into a gas to liquid or GTL conversion installation (42) to produce hydrocarbon products (44) and heat. The heat produced in the gas to liquid conversion installation is used to produce energy (20) to pressurize (16) the nitrogen in the nitrogen rich stream (34) to produce a pressurized nitrogen rich stream (22). The pressurized nitrogen rich stream (22) is passed into a natural oil reservoir (18) to enhance the recovery of oil (24) from the reservoir.