Annually around 250 million people worldwide undergo major surgery, including 2 million people in Australasia. Most patients will receive intravenous fluids during their operation, however, there is little evidence to guide clinicians in their choice of fluid or the optimum volume. Practices surrounding fluid administration vary greatly between clinicians. In the past, large volumes of intravenous fluid were often given to patients, however, recent small trials suggest that a more restrictive approach to fluids may reduce tissue swelling and improve patient recovery. This study is designed to provide a definitive answer to the question of how much fluid should be used, by measuring the effects of fluid restriction on patient-centred outcomes following major abdominal surgery. In New Zealand and Australia, 2800 patients will participate in this study to determine if a restrictive fluid strategy leads to reduced complications and improves survival when compared with a liberal fluid strategy.