Prosecutors in Singapore are seeking a 20-year jail term for disgraced Ocean Tankers founder Lim Oon Kuin for cheating and forgery following the collapse of his once-powerful oil trading company with huge debts.

The 82-year-old tycoon is due to be sentenced on 18 November. Prosecutor Christopher Ong is calling for a long term of imprisonment because of the “unprecedented” nature of the scandal that rocked Singapore’s reputation as an energy trading hub, Bloomberg reported.

Lawyers for Lim, best known as OK Lim, and who appeared in court in a wheelchair on Tuesday, are seeking a seven-year jail term after he was found guilty in May of cheating HSBC Holdings of $111.7m by instructing an employee to forge documents.

The now-defunct oil trader Hin Leong Trading was estimated to owe $3.5bn in debt to 23 banks at the time of its collapse after a plunge in oil prices in 2020. Lim hid huge losses from speculation in oil futures and sold oil inventories that were used as collateral for loans.

Lim, his son and daughter filed for bankruptcy this week after agreeing to pay $3.59bn to the liquidator and HSBC to resolve civil lawsuits against him and his family.

Several of the family’s properties in upmarket residential districts of Singapore have been sold, bringing in about $75m. More than 140 vessels from small coastal product tankers to VLCCs have already been sold off.

Hin Leong was founded in 1973 and its demise has been described by prosecutors as “one of the world’s largest collapses of an oil trading firm”.