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.

Here is a step-by-step guide to painting over creosote:

1. **Cleaning the Surface**: Begin by thoroughly cleaning the fence using a solution of warm water and a mild detergent to remove any dirt, grime, or loose particles from the creosote-treated wood.

2. **Sanding**: Lightly sand the fence to create a rough surface that will help the paint adhere better. Be sure to wear protective gear such as a mask and goggles to avoid inhaling any creosote particles.

3. **Priming**: Apply a high-quality oil-based primer that is suitable for use on creosote-treated wood. This will help create a smooth and uniform surface for the paint to adhere to.

4. **Choosing the Right Paint**: Select an acrylic latex paint or oil-based paint that is compatible with the primer and suitable for exterior use. Ensure that the paint is specifically formulated for use on treated wood.

5. **Applying the Paint**: Use a high-quality brush or roller to apply the paint evenly in smooth, overlapping strokes. It is recommended to apply at least two coats of paint for optimal coverage and durability.

6. **Maintaining the Fence**: To prolong the life of the paint job, consider applying a clear sealant or topcoat to protect the painted surface from UV rays, moisture, and other environmental factors.