Two percent of adults command more than half of the world's wealth, while the bottom 50 percent possess just 1 percent, according to a UN development institute study released Tuesday.

While income is distributed unequally across the globe, the geographical spread of wealth -- which includes property and financial assets -- is even more skewed, the study by the World Institute for Development Economics Research of the UN University showed.

"Wealth is heavily concentrated in North America, Europe and high-income Asia-Pacific countries. People in these countries collectively hold almost 90 percent of total world wealth," the survey said.

The Helsinki-based institute said this was the first global research on the topic, for which there is only limited data. The study is based on figures from 2000.

Institute director Anthony Shorrocks said if the world's population was reduced to a group of 10 people, one person would hold US$99 and the remaining nine would share US$1.

"The superrich are even more grotesquely rich than 50 years ago," he said.

According to the study, a couple in 2000 needed US$1 million in capital to number among the richest 37 million people in the world, the top 1 percent. More than half of that group lives in the United States or Japan.

"The United States and Japan stand out because they have large populations and high average wealth. Although Switzerland and Luxembourg have high average wealth, their populations are small," Shorrocks said.

Average per capita net assets in Japan were US$181,000, while in the United States the average was US$144,000.

The study found that net assets of US$2,200 per adult would put a household in the top half of the wealth distribution.

At the bottom of the list came nations such as the Democratic Republic of Congo and Ethiopia, with capital of less than US$200 per head.

Still, many in the wealthy West are house-poor, with assets well below this number due to mortgages and other debt.

"Many people in high-income countries have negative net worth and -- somewhat paradoxically -- are among the poorest people in the world in terms of household wealth," the report said.