This excerpt taken from the SIRI DEF 14A filed Apr 30, 2009.
Who are the principal owners of SIRIUS XMs stock?
The following table sets forth information regarding beneficial ownership of our common stock as of April 29, 2009 by each person known by us to be the beneficial owner of more than 5% of our outstanding common stock. In general, beneficial ownership includes those shares a person has the power to vote or transfer, and options to acquire our common stock that are exercisable currently or become exercisable within 60 days. We believe that the beneficial owner of the common stock listed below, based on information furnished by this owner, has sole investment and voting power with respect to these shares.