The three units are the Maersk Exerter, Maersk Enhancer and Maersk Endeavour.
Maersk Contractors will continue to operate the rigs on behalf of the new owners until the existing contracts end.
Maersk Contractors is currently in the process of building eight drilling rigs for delivery between 2007 and 2010, with several of these expected to be deployed in the North Sea.
Northern's three new units are all 300-foot independent cantilever rigs built in 1981 and 1982.
