Drop-on-demand devices are the heart of most modern ink jet printers. The fluid dynamic process during drop ejection is complex with time-dependent fluid interface disruptions. Based on computations with a generic problem configuration, the present work attempts to provide an insight into the drop ejection behavior for establishing general design rules in device development. The computational results show that the volume of ejected drop is very close to the volume of fluid pushed through the nozzle by an actuation pulse. The speed of the ejected drop is typically between one third and two thirds of the average velocity of the fluid pushed through the nozzle during actuation. The conditions for obtaining various (desirable or undesirable) drop shapes immediately after ejection are examined. The cases when drops may not be successfully ejected are also discussed.