If the creosote is well aged, not oily, you can apply oil base primer then paint. I recommend you power wash the fence and use a good environmentally friendly soap. A stiff scrub brush might be used for oily deposits.
After a good washing the woods pores will be opened up. At this point you could use a solid colored oil base stain instead of paint.
Test a area for stain or primer penetration before proceeding. A primer might discolor if some creosote is still active in the wood. Allow this coat to dry then apply another to seal the discolored areas.