The capillary siphon is a device capable of transporting a liquid from a higher level to a lower level by capillary action under gravity. The device is usually configured in an inverted U-shape with an intake end and a discharge end. However, to the authors' knowledge, the prior arts have not disclosed a process or apparatus that utilizes the capillary siphon action to transfer a liquid into a different liquid from a lower level to a higher level. In this paper, a porous medium, which preferentially has a higher wickability with respect to the first liquid than to the second liquid, is disposed in a siphon fashion with the first or intake end contacting the first liquid and the second or discharge end contacting the second liquid. A net amount of the first liquid was observed to be pumped into the second liquid. The aforementioned novel device functions as a passive pump, and could find applications in many systems such as portable direct methanol fuel cells and drug delivery systems. The device with these potential applications is termed as the "biliquid capillary siphon". The biliquid capillary siphon was successfully tested using several typical wick materials such as fiberglass, ceramic, polyethylene and PTFE under both dynamic and quasi-equilibrium states. (c) 2005 Elsevier Ltd. All rights reserved.