The problem arises of how to control a plurality of hydraulic pumps to achieve desired performance criteria, such as reduced wear and/or power consumption. The hydraulic pumps are operated in a hydraulic system for delivering hydraulic fluid to a hydraulic motor in a cryogenic pumping apparatus in an engine system fuelled with a gaseous fuel. A controller is operatively connected with the plurality of hydraulic pumps and is programmed to periodically determine a priority for each hydraulic pump as a function of predetermined criteria such as respective cumulative pumping cycles. Higher priority hydraulic pumps are operated before lower priority hydraulic pumps, that is in descending order of priority, to supply hydraulic fluid to the hydraulic motor. Hydraulic pumps are selected to operate according to the desired performance criteria.