Three people who gained their fortunes through Koch Industries Inc., as well as the founders of Continental Resources Inc. and Kinder Morgan Inc. (KMI), are among the wealthiest U.S. oil and gas tycoons, according to a ranking by Wealth-X.

The ranking, issued on Tuesday, updates a listing that was released by global researcher Wealth-X in January.

Koch Industries co-owners and brothers led the survey, with David Koch at No. 1 ($47.9 billion) and Charles Koch, No. 2, whose fortune is slightly lower at $47.8 billion. Their wealth is estimated now to be about 14% more than at the start of the year.

"Their combined fortunes, which far outweigh the combined net worth of the eight other U.S. oil tycoons in the Wealth-X ranking, rose by 14% between June 2014 and May 2015 through a portfolio of diversified business interests," the survey said.

Harold Hamm, who founded Continental, is No. 3 on the list, despite paying almost $1 billion to secure a divorce earlier this year (see Shale Daily,Jan. 9). His net worth of $11.8 billion is down 36%. Close behind is KMI CEO Richard Kinder at No. 4, whose net worth is estimated at $11.6 billion, 26% higher.

George Kaiser, a leading philanthropist, moved into the No. 5 spot with a fortune estimated at $10.6 billion, derived in part from his ownership of privately held producer Kaiser-Francis Oil Co. His wealth is down about 20% from January. Elaine Tettemer Marshall, No. 6, is worth about $8.8 billion, 13% higher than in January. Her fortune also is derived from Koch holdings that were willed to her by her late husband E. Pierce Marshall and father-in-law J. Howard Marshall.

Energy Transfer Partners LP CEO Kelcy Warren debuted on the list at No. 7 with a fortune estimated at $7 billion, 40% higher than in the previous survey.

The final three on the Top 10 ranking are children of the late Dan Duncan, who founded Enterprise Products Partners LP. Each has a fortune estimated at $5.7 billion: daughters Milane Frantz and Randa Williams, and son Scott Duncan. The Duncan fortunes are about 8% lower than in the previous ranking.