Cardiff Marine is in advanced talks with Jiangsu Rongsheng Heavy Industries in China to build five tankers for around $375m, according to reports.
The Greek firm is believed to be negotiating for two very large crude carriers for $97m each, and three Suezmax tankers at around $60m each.
Another Greek ship management company, Thenamaris, is also considering ordering two Suezmaxes at Rongsheng, with the option to build two more.
Industry analysts said they expected the shipyard to deliver the tankers in the second half of 2010.
Rongsheng is planning for a Hong Kong listing this year.