New in situ combustion (ISC) method variants hold much promise in the way of ultimate oil recovery and recovery rates. The interactions of thermal and reaction waves for ISC recovery of heavy oils are here investigated numerically. A set of dimensionless screening parameters is developed in order to investigate important ISC phenomena, i.e. ignition delay time, flame thickness and propagation, ultimate recovery, and recovery efficiency. Defining a heavy oil Damkohler number (Da(O)) allows the identification of three performance regions of ignition delay: thermal diffusion limited, chemistry limited, and oxygen supply limited. There exists also a coke Damkohler number (Da(C)) threshold for the combustion wave to propagate or else extinguish. The ISC process efficiency and recovery rate are observed to be functions mainly of the Da(C) number and less so of the Da(O) number. (C) 2013 Elsevier Ltd. All rights reserved.