In the previous century, hydraulic systems have been developed with the goal to successfully perform a specific function, while energy consumption remained an afterthought. In recent years, efforts have been made to modify the last century architectures to increase system performance. Functionality has been added to the hydraulic systems without changing the base technology. As a result, current valve controlled hydraulic systems are experiencing an upward trend of increasing complexity. The aim of this thesis was to demonstrate the importance of using dynamic mathematical models to appropriately design, size and simplify hydraulic system architectures for mobile machinery. Dynamic simulation models with measured representative duty cycles have been used to design and size efficient, yet simple, hydraulic system architectures for a combine harvester, and the hydraulic models were developed using MATLAB/Simulink RTM. The hydraulic systems on a combine harvester were chosen as examples and the design methodology used in this work can be applied to hydraulic systems on any mobile machine. The selected hydraulic systems on the combine harvester were the propulsion, reel drive, header lift. These systems were designed and sized using dynamic simulation models and compared to the current state of the art systems. The combined power savings of the novel systems over the current systems is 11.6 kW during an average harvesting condition for the combine harvester 11.6 kW of additional cooling power is saved. Therefore, the novel systems will require 11.6 kW less cooler power. This means the total power savings of the proposed systems is about 23 kW. A novel low-pressure system showed improvement of 7.54 kW over traditional low-pressure systems.