Preliminary results of a proton nuclear magnetic resonance study of water and oil drainage under gravity through a sand column are reported. Evolution of the proton magnetization and its spin–spin relaxation time T2 are given as functions of drainage time. It was found that the bulklike fraction of the liquids drains out quickly, while the pendular and surface fractions drain slowly until an equilibrium is reached. The “undrainable,” residual liquid fraction was observed to be ∼6% and ∼48% of its initial value for water and light oil, respectively. The proton T2 of water and oil in different environments are analyzed by employing the fast exchange model. This method of monitoring the drainage of two liquids can be easily adapted to study the spacial and temporal evolution of the liquids in the presence of a gas phase. © 1997 American Institute of Physics.