A control system for a continuous liquid phase hydroprocessing reactor having an upper zone of gases and a substantially larger lower zone of liquids surrounding a catalyst, comprising: (a) an indicator located on said reactor, (b) means for sensing the quantity of liquid in said reactor; (c) an indicator reading obtained from said sensing means; (d) means for converting said indicator reading to an indicator signal; (e) a computer to receive said indicator signal; (f) means for transmitting the indicator signal to said computer; (g) a software program to interpret said indicator signal and make adjustments based on said indicator signal; (h) means for converting said adjustments to an adjustment signal; (i) means for transmitting said adjustment signal; (j) a hydrogen control valve, located upstream from said reactor, which adjusts the amount of hydrogen going into a reactor feed; (k) means for interpreting the adjustment signal at said hydrogen control valve; and (l) means for adjusting said hydrogen control valve based on said interpreting means.