A dual engine color printer has two print engines, one for printing each side of the sheet. Each engine comprises a single multi-color set of printing drums—a set meaning a PIP drum, a blanket and an impression drum. A scheduling method is provided for imbalanced duplex printing of sheets in a print job, imbalanced meaning that the two sides of the sheets requires different numbers of colors. This conventionally leads to a situation in which one engine would have to wait until the other engine has finished. The method comprises feeding the sheets in sequence between the print engines, and alternating, over the sequence of engines, between printing the upside of a sheet followed by the down side for even sheets and the downside followed by the upside for odd sheets. Thus the two print engines are utilized full time and are not left idle while waiting for each other.