Chile, UAE, Singapore, Azerbaijan, Ireland and Norway claim top rankings on the latest transparency index, published by SWF Institute. At the bottom of the ranking is Venezuela, Oman, Nigeria, Mauritania, Kiribati, Iran, Brunei and Algeria.

The Linaburg-Maduell index is calculated with 10 principles -- such as whether the fund provides up-to-date, independently audited annual reports, or whether it provides clear strategies and objectives. It also gives points on whether the fund gives ownership percentage of company hodlings, total market value, returns and management compensation.

Enhancing transparency is a key task for sovereign wealth funds, whose often opaque operations have come under heavy criticism by some Western politicians who suspect them of investing with political, rather than commercial, motives.

In fact in the recent meeting of the world's leading sovereign wealth funds, only Norway, Chile, New Zealand agreed in advance to speak to Reuters on the sidelines; when contacted on the ground China also spoke. Others either declined to comment at all or did not return email.

(Source: SWF Institute; www.swfinstitute.org)