Sydney property developer Denis O'Neil and his company Addenbrooke have lost a court battle to reclaim an $8 million investment in Cascade Coal, where he claimed he was not informed of former NSW Labor minister Eddie Obeid's secret holdings in Cascade Coal.

Mr O'Neil claimed he was misled because he was not told his investment in Cascade Coal in 2010 would be used to partly pay for a $28 million share-raising in 2010 that was used to buy out the Obeids' secret interest in the company and its mining joint venture over the Obeid family's Bylong Valley farm.