Aston Villa are the only Championship side to have spent more than Sunderland in agent fees between February 2017 and 31 January 2018, figures released by the FA have shown.
The Black Cats paid out £4,370,897 to registered intermediaries during that time.
Steve Bruce's Villa paid out £5,510,180, with Ipswich Town the league's lowest spenders. They paid out just £241,969.
Sunderland spent just over £1 million in the summer transfer window, despite the sale of Jordan Pickford to Everton.
Only six Championship clubs were estimated to have spent less.
Sunderland have, however, experienced another year of extraordinarily high turnover when it comes to players.
Since the end of last season they have completed 15 incoming deals, a variety of loans, free transfers and low-cost permanent additions. There have also been 15 outgoing deals completed in that time, including a raft of loans.
They are set for another busy summer with Chris Coleman that the squad will need 'regenerating', no matter what division the Black Cats find themselves in.
The full figures released by the FA can be seen here.