A control system for controlling a vapor recovery system that recovers vapors expelled during refueling of at least one vehicle at one or more fuel dispensing points and returns the vapors to an underground storage tank in a service station environment, the system comprising: a vapor return passage, at least one air to liquid regulator valve associated with the or each fuel dispensing point, the air to liquid regulator valve being configured to regulate, subject to presence of a constant negative pressure within said vapor return passage provided for withdrawing vapor from the or each air to liquid regulator valve, a proportional amount of vapor recovered through the fuel dispensing point for a given amount of fuel that is dispensed through the or each fuel dispensing point; a vapor pump that is in fluid communication with the or each air to liquid regulator valve, the vapor pump having an inlet side and an outlet side; said vapor return passage being in fluid communication with the or each air to liquid regulator valve and the vapor pump; a controller operatively connected to the vapor recovery system, said controller being adapted: a) to monitor at least one parameter of the vapor recovery system, and hence b) to determine an amount of current to be provided to a variable speed electric motor that drives said vapor pump, in order to c) maintain a substantially constant pressure level, independent of flow rate, in a first portion of the vapor return passage that is disposed between the inlet side of the vapor pump and the or each air to liquid regulator valve, characterised in that said monitored parameter of the vapor recovery system is an estimated pressure difference between an inlet side and an outlet side of the vapor pump, derived when in use from two actual parameters in combination namely (a) a motor torque; proportional to a current developed in a non-energized winding of the variable speed motor that drives the vapor pump, and (b) a motor rate of rotation; proportional to a stepping rate for current applied to one or more windings of the variable speed motor; said combination being converted within the controller into an estimated pressure value, thereby allowing the controller to regulate the estimated pressure within the first portion of the vapor return passage independently of flow rate. a) to monitor at least one parameter of the vapor recovery system, and hence b) to determine an amount of current to be provided to a variable speed electric motor that drives said vapor pump, in order to c) maintain a substantially constant pressure level, independent of flow rate, in a first portion of the vapor return passage that is disposed between the inlet side of the vapor pump and the or each air to liquid regulator valve, characterised in that said monitored parameter of the vapor recovery system is an estimated pressure difference between an inlet side and an outlet side of the vapor pump, derived when in use from two actual parameters in combination namely (a) a motor torque; proportional to a current developed in a non-energized winding of the variable speed motor that drives the vapor pump, and (b) a motor rate of rotation; proportional to a stepping rate for current applied to one or more windings of the variable speed motor; said combination being converted within the controller into an estimated pressure value, thereby allowing the controller to regulate the estimated pressure within the first portion of the vapor return passage independently of flow rate.