Laboratory measurements of wettability of oil may not accurately reflect the wettability of the actual reservoir system. This can cause an under or over estimate of hydrocarbon volumes present. Such errors can be decreased by measuring the wettability of the crude oil, brine solid system directly. The purpose of this research was to develop a way of converting the wetting balance method for measuring the wettability of a crude oil, brine solid system directly. This included developing a method of sampling and storing crude oil with minimum alteration to wettability characteristics. Tests on 10 separate crude oils showed that most Australian reservoirs are water wet with one oil wet and one intermediate wet. Silica, the predominant mineral present, was found to be the most water wetting of all minerals. The wettability of the crude oil, brine solid system was also found to be dependent upon velocity of the front of hydrocarbons produced from the reservoir because the contact angle was velocity dependent. The reservoir condition wetting tool may be a useful research tool but it is unlikely to be embraced by the petroleum industry because of the cost of testing. 7 figs., 7 tabs.