An experimental study was carried out concerning the optimization of catalyst type, operating conditions, addition of water and hydrogen for use in the THAI-CAPRI process and is reported. Three feeds namely, THAI field oil, Combustion Cell Oil (CCO) and n-decane were used in the presence of catalyst or an inert medium for comparison. Experiments were carried out using micro-reactors containing 5 g catalyst under different temperatures, pressures and gas environments. It was found that there was a trade-off in operation temperature between upgrading performance and catalyst lifetime. At higher temperatures of 500 °C led to an average of 6.1 °API upgrading , however, the catalyst lifetime was limited to 1.5 hours. Operation at 420 °C was found to be a suitable compromise, with upgrading limited up to 3 °API, with catalyst lifetime extended to 77.5 hours. From the results of the current study it can be said that by careful control of the temperature and oil flow rate in the in-situ CAPRI process, additional upgrading compared with the THAI process alone may be effected, resulting in a more valuable produced oil, which is easier to transport and could be further processed into distillates.