Abstract: To increase the product value out of a crude barrel, some refineries produce Group III lube base oil (LBO) through catalytic hydroprocessing, in addition to the conventional fuels, such as gasoline, diesel, kerosene etc. The optimization of a refinery with fuels and lubes portfolios is considered a challenge since there are several tradeoffs which need to be addressed. The main challenge is the crude selection, since the conventional fuels qualities are determined by the physical properties of the crude oil, while the lube base oil quality is mainly determined by its viscosity index (VI), which strongly depends on the chemical composition of the processed crude oil. Additionally, the operating conditions such as the hydrocracking conversion is important in determining the yield and quality of the lube base oil. Moreover, the split of the downstream feedstock, such as Heavy Vacuum Gas Oil (HVGO) and Unconverted Oil (UCO) need to be determined and distributed to several conversion units in the refinery. The purpose of this thesis is to propose an overall optimization methodology for a local refinery in Bahrain with a lube base oil processing capability, which has been processing two types of crudes only. Different than the limited works available in the literature, the current thesis has explicitly considered a complex refinery setup with several downstream feedstock split to be optimized. In addition, the inclusion of the Fluid Catalytic Cracking Unit (FCCU), which been ignored in previous studies, render the current formulation NLP. This is done by employing a crude classification model based on the Hydrocracking Unit (HCU) feed VI, and taking into account the change in VI and yields besides the other conventional bulk properties. This will optimize the selected crude types that maximize the products value and the overall refinery margin. The results showed that allowing crude selection in the studied refinery can increase the contribution margin by US$30 million per month when compared to the current operation of processing two crudes only. Using the VI model to predict how VI changes through the hydrocracking and lube base oil units is required to ensure that final LBO quality is met. It has proved that crude selection changes with the required specification of LBO VI and the hydrocracking conversion. When Conversion decrease from 80% to 75%, volume of paraffinic crudes increases by 3% and 16% for VI spec at 120 and 125, respectively.