The present invention relates to a downhole artificial lifting system for introducing fluid into a production casing from an annulus arranged outside the production casing. The production casing has an axial extension and a casing wall with a wall thickness, and the system comprises the production casing which at a first part is surrounded by an intermediate casing creating the annulus which is downwardly closed, and a fluid delivering means pumping fluid into the annulus. The invention also relates to a tool for use in the system and a method.