Abstract: A bucket for use in a swinging bucket centrifuge. A core holder is located between two end chambers, with the annular space between the core holder and the bucket sidewall maintaining the chambers in fluid communication. Windows at each end of the bucket allow fluid collections to be monitored. This enables more accurate data to be obtained regarding the effect of fluids of different specific gravity on a fluid saturating a sample. For example, to obtain data allowing a more accurate modeling of reservoir conditions in an oil field impacted by both gas and water displacement, the amount of oil expelled from a rock sample by gas under pressure and temperature conditions simulating those in the reservoir is measured and, after replacing the gas with water, the amount of oil expelled by water under simulated conditions is measured.