Cylinder deactivation enables improvements in fuel economy in spark-ignition engines by reducing pumping losses during part load operation. The efficiency benefits of a new intake valve system that enables cycle-by-cycle deactivation of different cylinders is investigated in this study. The system minimises the need for throttling by varying the fraction of strokes that are deactivated in order to vary engine output. The intake valve system involves two intake valves in series, with a fast solenoid-actuated valve upstream of a conventional cam-actuated intake valve. Compared to conventional cam-actuated valves, the new valve system has potential to achieve very rapid closing rates with a high degree of flexibility in respect of the timing of inlet valve closure. The fuel economy benefits provided by a number of valve control strategies are evaluated using a one-dimensional modelling approach, considering a vehicle following the New European Drive Cycle. The analysis indicates that the volume between the two valves should be kept to less than four times the cylinder clearance volume. Use of the intake valve system to control load by cycle-to-cycle cylinder deactivation practically eliminates the need for throttling and is predicted to offer a very substantial improvement in fuel economy, achieving as much as a 43% fuel saving over the New European Drive Cycle, compared to throttled engine operation. Use of flexible cylinder deactivation also affords fuel savings and thermal management benefits compared to more conventional cylinder deactivation schemes in which a fixed proportion of the cylinders, typically one half, are deactivated at one time. The use of the valve system to make fine adjustments to the intake valve closure in order to control engine load without any throttling is also discussed.