In a statement, the company said among nearly 30 companies, one belongs to its parent company, PTT.
"The purpose was not to launder money or evade tax, but to support management flexibility and reduce investment risks. The Cayman Islands' laws allow easy process for company registration, capital increase and reduction, as well as closure with low operating fees," it said.
It added that this is in line with other global oil companies' practices.
It also said that it has opened no account with any bank on the Cayman Islands. All bank accounts linking the company and subsidiaries to banks on the islands are opened with Thai banks or banks in other countries, strictly under the rules of the Bank of Thailand and other countries' central banks.
"All the accounts are managed by the headoffice, under the supervision of the board of directors for transparency," it said.
It added that all business units, but Taninthayi Pipeline Co, registered in the Cayman Islands were audited by the Auditor General's Office. Taninthayi Pipeline, owned 19.4 per cent by PTTEP and the rest by PTT, is audited by Ernst & Young.