The politically conservative Koch brothers top the list for the richest oil barons in the world, according to Wealth-X, an information resource on the ultra-wealthy.

Although oil prices have plummeted by more than 50 percent in less than a year, the fortunes of many of America’s prominent oil industry billionaires have risen, according to a Wealth-X list of the top 10 richest U.S. oil tycoons released Tuesday.

At the top of the list are the billionaire oil baron Koch brothers, Charles and David, each of whom has a net worth of nearly $45 billion. Their wealth increased by 7 percent since last June, according to Wealth-X. The increase is due to the fact that their industrial conglomerate, Koch Industries, has a large, diversified investment portfolio with significant holdings in pipelines and refineries, but is not a major oil producer.

Another major shareholder of Koch Industries, Elaine Marshall, claimed the sixth spot on the list with a net worth of $8.3 billion. She is one of four female oil barons who appear on the list.

The eight, ninth and tenth spots are held by the Duncan sisters, Milane Frantz, Randa Williams and Dannine Avara, each of whom has $5.5 billion in assets. Each of the three daughters of the late Dan Duncan, who built an energy pipeline empire, lost 11 percent of their wealth since last June, when oil prices began falling.

George Kaiser, the founder of BOK Financial Corporation in Tulsa, Ok., holds the third spot with $13.2 billion.

Claiming the fourth spot is Richard Kinder, chairman of the pipeline giant Kinder Morgan. He had the biggest increase of the 10 with a 23 percent gain since last June to reach $11.3 billion. The bulk of the company’s money comes from fixed contracts with customers who transport fuel over the company’s pipelines.

Harold Hamm, the CEO of Continental Resources, is the biggest loser in the group, having lost nearly half of his wealth over the past six months due to the fall in oil prices and a costly divorce, Wealth-X says. He holds the fifth spot with $9.3 billion.

In the seventh spot is Ray Hunt, the richest of the sons of Texas oil wildcatter H.L. Hunt. Wildcatters drill oil exploration wells in areas not known to have oil, which sometimes produces rich wells. Hunt now has $5.6 billion after losing 7 percent since June, Wealth-X reports.