Abstract: A process to prepare a base oil having a viscosity index of above 80 and a saturates content of above 90 wt % from a crude derived feedstock by (a) contacting a crude derived feedstock in the presence of hydrogen with a catalyst having at least one Group VIB metal component and at least one non-noble Group VIII metal component supported on a refractory oxide carrier; (b) adding to the effluent of step (a) or part of the effluent of step (a) a Fischer-Tropsch derived fraction boiling at least partly in the base oil range in an amount effective to achieve the target viscosity index of the final base oil; and (c) dewaxing the mixture as obtained in step (b).