Do you mean oil on the outside of the plugs? That would mean a loose cam cover gasket. If the firing end of the plug is wet and black, then I would think only one would be oil covered - rare for all four plugs to show oil burning. If dry black then it's running rich.
In any event regardless of the colour, check for oil consumption - anything more than 1000 miles per quart is fine, or poor fuel economy. More diagnosis is needed.