The application of a new method for measuring velocity fields within a porous medium is presented. Fluid containing fluorescent microspheres is flowed through a transparent, refractive-index-matched column filled with 3.1 mm spherical beads. A planar laser beam illuminates a cross-section of the bed. Using a video camera and a frame-accurate videocassette recorder, the motions of the fluorescing particles are recorded as the fluid flows through the bed. Subsequently, the particles are tracked through a series of frames using a commercial image analysis software package. Because the particles move slowly compared to the video frame rate (30 frames per second), frame-to-frame particle identification is unambiguous. The time histories of the particle positions are used to calculate velocity components in the plane of the beam. Results are shown in which the velocity field within a full volumetric segment of a column is measured, and the averaging properties of the measured velocity field are discussed. The volumetrically averaged velocities are shown to be in good agreement with the superficial velocity. This technique is easy to automate and can be used to measure a wide range of velocities with high precision.