Many automotive transmissions, including automatic and hybrid transmissions, employ electro-hydraulics for gear shift, system cooling, and lubrication. Transmission oil budget refers to the process of dynamically distributing pressurized fluid from the pump into the sub-systems of the transmission. The oil budget will ultimately determine the transmission pump size and directly impact vehicle fuel economy. It will further affect the dynamic performance of the transmission. Due to large number of components, complex hydraulic circuits, and dynamic operating conditions, estimating transmission oil budget is extremely complex. To obtain a precise oil budget, we need to not only model each hydraulic component accurately, but also analyze the flow requirement in a dynamic fashion. This paper presents the modeling of the transmission hydraulic system and its application for oil budget analysis.