Which oil is to be used for air compressor as a lubricant?


We are using a  2.5 hp air compressor for water supply from a borewell of 270 ft depth, since the water table is not sufficient enough for using a submergible pump. Can you please tell us which grade of oil is to be used for such compressors as lubricant?  Since it is a local make we have not been given any booklet of specifications, etc. Please suggest.