This experimental study investigates the three-dimensional, time-resolved, incompressible flow field of a spatially oscillating jet interacting with a crossflow. A traversable stereo particle image velocimetry system is employed for plane-by-plane acquisition of the flow field data. Established methods are used for phase-averaging the results, thereby reducing stochastic noise and compensating for low sampling rates. The oscillating jet is emitted into a crossflow with its oscillation plane perpendicular to the direction of the crossflow. No streamwise pressure gradient is present. The trajectory of the sweeping jet is significantly shallower than that of a comparable steady jet in crossflow, due to faster decay of the jet velocity. A dominant streamwise, counter-rotating vortex pair is generated by the sweeping jet. The sense of rotation is opposite to the counter-rotating vortex pair generated by steady jets in crossflow. This causes the vortices to push each other toward the wall and enables them to prevail far downstream. The streamwise vortices appear in an alternating manner due to the oscillation of the jet. The distance between the segments of each streamwise vortex depends on the combination of oscillation frequency and convection imposed by the crossflow.