The characteristics of an in situ combustion process carried out on a light crude oil are different from those normally depicted by heavy oils or tar sands. The kinetics of such a process, however, are extremely specific to the oil investigated. Combustion tube tests are normally performed to evaluate the air or oxygen and fuel requirement parameters. The product gas compositions from combustion tube tests are also useful for evaluating field performance, as it is possible to evaluate the relationship between gas composition and the temperature profiles in the laboratory experiments. In field projects there is generally little information on temperature profiles, but the gas composition can be monitored. This study is based on the data (produced gas compositions, peak temperatures and post burn residues) provided by laboratory experiments on re-constituted cores from the Countess B and D pools. Through the apparent atomic hydrogen to carbon ratio, it was found that the overall kinetics of the combustion process for Countess B oil undergo a transition over a temperature range of 260$\sp\circ$C to 270$\sp\circ$C, and that a negative temperature coefficient region exists between 310$\sp\circ$C and 350$\sp\circ$C. The virtual absence of residual coke suggested that the hydrocarbon fuel is an asphaltenes type fraction.