This thesis describes the application of microprocessor engine management techniques to the control of the hydrogen/petrol engine. A discussion of the world's fuel resources and the need for energy conservation is followed by a review of the literature related to the use of hydrogen as a fuel. The concept of hydrogen supplementation is introduced and then the work of other researchers in this field is studied in some detail in order to establish the control requirements for hydrogen/petrol operation. A survey of the literature relating to engine management techniques precedes a description of the microprocessor-based controller which was developed for this work. Following this is a description of the engine calibration process which involves the use of specially developed surface-fitting and contour-tracing software. Steady-state operation in the hydrogen/petrol mode resulted in significant energy savings but poor driveability was obtained when the control system was fitted into a Ford Transit Crew Bus. Transient operation during the ECE-15.04 test resulted in a small fuel economy gain but the exhaust emissions exceeded the legislative limits. It was concluded that, although the steady-state performance showed promise, further development of the control system was required to meet the demands of transient operation.