Present knowledge of the distribution of thorium resources is poor because of the relatively low-key exploration efforts arising out of insignificant demand. There are two sets of estimates that define world thorium reserves, one set by the US Geological Survey (USGS) and the other supported by reports from the OECD and the International Atomic Energy Agency (the IAEA). Under the USGS estimate, USA, Australia and India have particularly large reserves of thorium.
Both the IAEA and OECD appear to conclude that India may actually possess the lion's share of world's thorium deposits. The Government of India's latest estimate, shared in the country's Parliament in August 2011, puts the recoverable reserve at 846,477 tonnes.
OECD assessment
India and Australia are believed to possess about 300,000 tonnes each; i.e. each country possessing 25% of the world's thorium reserves.[65] However, in the OECD reports, estimates of Australia's Reasonably Assured Reserves (RAR) of thorium indicate only 19,000 tonnes and not 300,000 tonnes as indicated by USGS. The two sources vary wildly for countries such as Brazil, Turkey, and Australia. However, both reports appear to show some consistency with respect to India's thorium reserve figures, with 290,000 tonnes (USGS) and 319,000 tonnes (OECD/IAEA).