In a method of recovering petroleum from underground formations penetrated by a production well, superheated steam and then hot hydrogen are injected by way of the well into a preheated formation zone next to the well. The hydrogen is injected under sufficient pressure to cause hydrogenation of the petroleum in the heated zone. The well is shut in and the hydrogen in the heated zone is allowed to "soak" for a period of time after which the pressure in the well is lowered and petroleum is recovered from the heated zone by way of the well. The cycle can be repeated a number of times.
By way of another well spaced from the production well, fluid under pressure is injected into said formations to drive petroleum in said formations between the two wells to the production well for recovery. Hydrogenation of the petroleum occurs as it is driven through the heated zone in the presence of the hydrogen therein.