A jet drop printer prints graphic information upon an oscillating printing medium. The printer has a row of jet forming nozzles which produce a row of spaced drop streams. The drops in the streams are selectively charged, deflected and caught, so that uncharged drops produce intelligible graphic information on the printing medium. The spacing between the jets is such that they cannot print contiguous traces upon an ordinary transported printing medium. Contiguous printing is accomplished by lateral oscillation of the printing medium. The oscillation of the printing medium causes each jet to be directed at a plurality of lateral printing positions on a sequential basis, and data representing printing information for the different printing positions is multiplexed into the drop switching system in synchronism with the oscillation of the printing medium.Oscillation of the printing medium may be accomplished by a web transport system including a cylindrical roller and an axially driven oscillator connected thereto. The roller has an internal cavity large in diameter at the midpoint of the roller and relatively small in diameter at the support points of the roller. This causes an axially varying roller cross-sectional area which reduces roller distortion at the relative high axial vibration frequency.