The ATI, published by donor advocacy group Publish What You Fund, found that most of the world's largest and most influential donor organisations continued to limit data on their aid spendings, despite signing on the International Aid Transparency Initiative (IATI), which is the only internationally agreed standard for publishing aid data.
Among the worst offenders included Germany's, France's and Japan's foreign offices, while the Bill & Melinda Gates Foundation also scored "very poorly" in the 2013 index.
"No matter how many international promises are made, no matter how many speeches there are around openness, a startling amount of organisations are still not delivering on their aid transparency goals," said David Hall-Matthews, Director of Publish What You Fund.
"Open data and transparency are becoming fashionable watch words, but we're checking if donors are really delivering, looking beyond high-level commitments and long-held reputations.
"We will continue to encourage organisations to release more data - but more is not enough. We also want to make sure that the information is useful," Hall-Matthews added.
For the first time, the ATI measured not only the quantity but also the quality of information published by aid donors. Unlike previous years, it awarded more points to agencies publishing information in formats that are easy to access, analyse and reuse - penalising those who released data in formats that were difficult to navigate.
The top ranking agency this year was the U.S. Millennium Challenge Corp. (MCC), an independent U.S. Government foreign aid agency that delivers large-scale grants to developing countries. China's Ministry of Commerce, which distributes foreign aid on behalf of the government, was ranked the lowest.
"MCC publishes its aid information in the IATI format, right down to results level; in contrast, there is no way to confirm even the total amount of aid provided by China, Hall-Matthews said.
In total, 41 of the 67 donor organisations surveyed scored "Poor" or "Very Poor". Meanwhile, just four agencies received a "Very Good" score, with five receiving "Good."
"It's not all bad though," said Hall-Matthews. "France and Japan (who both received "Very Poor" scores) have both committed to publishing their aid data to IATI by 2015 as part of the G-8 commitments, so there is time to correct this poor practice."
"Indeed, some donors have made real progress over the past year. It is great that they have released a lot more data - but that is not enough on its own. The development community now needs to make sure the information is as useful as possible."
The Top 10 Most Transparent Donor Organisations
1. U.S. Millennium Challenge Corporation (MCC) - Very Good
2. GAVI Alliance - Very Good
3. U.K. Department for International Development - Very Good
4. United Nations Development Programme (UNDP) - Very Good
5. World Bank International Development Association - Good
6. The Global Fund to Fight AIDS, Tuberculosis and Malaria - Good
7. African Development Bank - Good
8. Canadian International Development Agency - Good
9. Swedish International Development Cooperation Agency - Good
10. Asian Development Bank - Fair
The Bottom 10
58. Slovenia Ministry of Foreign Affairs - Very Poor
59. Germany Foreign Office - Very Poor
60. Italy Ministry of Foreign Affairs - Very Poor
61. Lithuania Minsitry of Foreign Affairs - Very Poor
62. CyprusAid - Very Poor
63. Bulgaria Ministry of Foreign Affairs - Very Poor
64. Hungary Ministry of Foreign Affairs - Very Poor
65. Malta Ministry of Foreign Affairs - Very Poor
66. Greece HellenicAid - Very Poor
67. China Ministry of Commerce - Very Poor