'The unique operation of the THAI (Top-to-Heel Air Injection) process, enables very high oil recovery and substantial in situ upgrading. Both thermal upgrading (non-catalytic) and also catalytic upgrading, in which a catalyst is emplaced along the horizontal producer well, were investigated 3D physical model experiments were conducted on virgin Athabasea tar sand bitumen to investigate dry and wet combustion performance These results were compared against those from a steamflood test, which was subsequently followed by injection. Excellent ignition, very stable combustion propagation and thermal upgrading of nearly 10degrees API were achieved using Athabasca tar sand: Additional upgrading was achieved using an in situ catalyst. THAI has the extra advantage that some hydrogen is generated in situ, providing further significant upgrading via hydroconversion. There are also substantial environmental benefits because of the large reductions in sulphur and heavy metals in; the produced oil: Furthermore, oil is produced without "displacement delay," immediately ahead, of the, combustion front: The oil recovery using THAI was greater than 75% OOIP.