Sullivan and new Hammers co-chairman David Gold, sold their interest in Birmingham last year, having previously owned 27 per cent of the Hammers 22 years ago.
Sullivan has now returned to take a 50 per cent stake in West Ham, with Icelandic bank Straumur holding the remaining half.
New boys: David Sullivan and David Gold pose at Upton Park
Click here to read West Ham's statement in full after the £105m takeover at Upton Park But despite describing their excitement at taking control of a clubclose to both of their hearts, Sullivan's estimation that the Hammersowe in excess of £100m and have limited incomings grabbed theattention.
Changes: David Sullivan at Upton Park
'We wouldn't buy this club at all if this wasn't West Ham. It makesno commercial sense for anyone to buy this club and it's amazing thattwo other people wanted to buy it.
'One is another West Ham supporter (Tony Fernandes) and the Italian(Massimo Cellino), I'm not quite sure if he looked at the booksproperly, but if he looked at the books he might have walked away.
'We've paid down some of the debt and injected some working capital but there's still more than £100m of debt.
'In that there's £50m owed to banks, there's £40m owed to otherclubs. There's not a penny to come in, they (the previous owners) haveborrowed against the next two years of season-ticket money. Thesponsors have paid 70 per cent of their three-years up front.
'In addition there's the club's settlement to (former manager) Alan Curbishley, so the real debt is about £110m.'
Click here to read Martin Samuel's exclusive Sportsmail interview with Karren Brady
Time for change: David Gold and Karren Brady arrive at Upton Park
The new Hammers ownership team revealed their first achievement hadbeen to avert the need to raise £20m in the next two transfer windowsto keep the club afloat - £8m in January and £12m in the summer.
Gold told Sky Sports: 'The first thing we needed to do was not tobring in new players, the first thing was to make sure no players left.Up until a month ago you constantly read and saw on TV that the currentowners would have to sell their best players to stay in business.
'We can reassure fans who were terrified that they were going tolose two or three of the best players that that is now not going tohappen.'
Backs to the walls: West Ham are in a relegation fight
Sullivan believes the club's future would be brighter if they couldmove to the Olympics stadium in east London after the Games in 2012,but admitted they would have to reach some kind of compromise over therunning track.
Asked whether they would be happy to live with the track around thepitch, he told Sky Sports News: 'Ideally no, but there may be a way wecould lay the running track for three months or something. It may becheaper to build a running track somewhere else. I don't think runningtracks work, particularly behind the goal. The customers are so farback it doesn't work.
Click here to read Neil Moxley's lowdown on Sullivan and Gold's stint at Birmingham 'We don't want to buy (the Olympic Stadium), we want to rent it. TheGovernment promised to keep it alive for 30 years, it's going to costthem more to keep it alive. With us it's going to cost them nothing -we would pay all the running costs.'
Sullivan's deal sees him taking strategic and operational controlof the club with his 50 per cent stake, while he has an option on theremaining shares which will exist for a four-year period.
Safe: Gianfranco Zola will stay in charge of West Ham
Nevertheless, with the club in a perilous state, he is insteadhopeful of attracting a team of wealthy investors to help get theHammers back on track.
'We own 50 per cent of the club but I have an option on the other50. I would share that with David but I would like to have four or fiveWest Ham supporters with lots of money to come in.
'The debts here are so large that most Englishmen can't carry themso we would like to share them with others and help take West Ham tothe next level.
Next move? West Ham could relocate to the Olympic Stadium
'The bank Straumur own the other 50 per cent right now and myoption to buy is for anytime in the next four years. Our preferredoption is that we find other people who want five or 10% and we will goto Tony Fernandes, who was one of the others interested in buying theclub.
'If you imagine a government of national unity in national crisisthis is the board equivalent and we want people to come in and help digthe club out of that.Every stone you turn is a negative to the cash flow of the club and viability of the club.
'They (the previous owners) have done a fantastic job of keepingthe club alive but the cost is we are taking over an incredibly badsituation. However, we will sort it out because we are good at it.'
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