Process to prepare a haze free base oil having a cloud point of below 0° C. and a kinematic viscosity at 100° C. of greater than 10 cSt by performing the following steps: (a) hydroisomerisation of a Fischer-Tropsch synthesis product, (b) isolating one or more fuel products and a distillation residue, (c) reducing the wax content of the residue by contacting the feed with a hydroisomerization catalyst under hydroisomerization conditions, and (d) solvent dewaxing the product of step (c) to obtain the haze free base oil.