Among the seminar titles were "The Moral Foundations of Capitalism," "Corporations and the Limits of Criminal Law" and "Terrorism, Climate & Central Planning: Challenges to Liberty & the Rule of Law."
Leading the list of sponsors of the 109 seminars identified by the Center were the Charles G. Koch Charitable Foundation, The Searle Freedom Trust, ExxonMobil Corp., Shell Oil Co., pharmaceutical giant Pfizer Inc. and State Farm Insurance Cos. Each were sponsors of 54 seminars.
Sponsors pick up the cost of judges' expenses, which often include air fare, hotel stays and meals. The seminars in the Center's investigation took place from July 2008 through 2012.
About 11 percent of the more than 1,700 federal judges in the United States reported attending one or more of the seminars over the period, according to disclosure forms reviewed by the Center.
Roughly three-fourths of the more than 800 sponsors listed in documents were individuals, including a number of judges who took trips, raising the possibility that they may have offset the cost of the seminars with their donations. Most of the remaining underwriters were companies and foundations.
Determining exactly how much was paid by which sponsor is difficult to determine - amounts are not required to be reported under the disclosure rules.
Judicial conferences are billed as educational retreats intended to improve judges' understanding of the law and economics.
Two schools - George Mason University, located in Virginia just outside Washington, D.C., and Northwestern University based in Evanston, Ill., - hosted more than two-thirds of the seminars.
The most-traveled judges, according to reports filed online by the judges, were U.S. District Judge Charles R. Wolle of the Southern District of Iowa and Chief Judge Thomas B. Bennett of the Northern District of Alabama Bankruptcy Court. Each reported attending nine seminars.
Wolle is a "senior status" judge, meaning he is semi-retired. He did not respond to requests for comment.
The next-most-traveled judges were:
U.S. District Judge Manuel L. Real of the Central District of California and Judge Diarmuid F. O'Scannlain of the U.S. Court of Appeals 9th Circuit, covering the Western states, who each took eight trips;
E. Grady Jolly, a federal appeals court judge for the 5th Circuit which includes Texas, Louisiana and Mississippi, and U.S. Bankruptcy Judge Michael B. Kaplan of the District of New Jersey, who each took six trips.
In an email, Kaplan wrote that the "seminars offer a valuable opportunity for new judicial appointees to enhance their knowledge and skills in complex areas of the law," including economics. O'Scannlain declined to comment for this story.
Wolle, Real and O'Scannlain are all listed as seminar sponsors, though records do not indicate how much they contributed.
In April 2009, Jolly traveled to Northwestern University to attend the "Criminalization of Corporate Conduct" seminar sponsored by the American Petroleum Institute, the U.S. Chamber of Commerce and 13 other funders.
Last August, Jolly wrote the majority 2-1 opinion declaring that the Environmental Protection Agency broke the law when it rejected a Texas emissions cap generally supported by the fossil fuels industry.
Jolly, who did not respond to requests for comment, sided with two of the petitioners in the suit - the American Petroleum Institute and the U.S. Chamber.
George Mason University's Law & Economics Center hosted 45 seminars while Northwestern University's Judicial Education Program hosted 29. The remaining top five conference hosts, including The Sedona Conference and the Foundation for Research on Economics and the Environment (FREE), collectively organized 28 conferences.
Billionaire brothers Charles and David Koch, major supporters of conservative causes, and their foundations have given millions to George Mason University. As the Center recently reported, the George Mason University Foundation received $4.4 million in 2011 from the Charles Koch Foundation, making up 15 percent of its revenue that year.
Officials from the Charles G. Koch Charitable Foundation did not return phone calls seeking comment for this report.
The Searle Freedom Trust, a foundation advocating "economic liberty" which regularly donates to conservative groups like the Cato Institute and the American Enterprise Institute, contributed a combined $400,000 to George Mason's judicial education programs in 2010 and 2011.
Seminars at Northwestern are hosted by the school's Searle Center on Law, Regulation, and Economic Growth. The think tank, according to its website, was founded in 2006 thanks to a "generous grant" from Daniel C. Searle, the late pharmaceutical industry executive.
In 2009, the foundation gave $200,000 to Northwestern's Searle Center for its judicial education program.
Records show corporate sponsorship at Northwestern was highest from 2008 through 2010, when a man named Henry Butler - now in charge of George Mason University's Law & Economics Center - ran the Searle Center.
Daniel Rodriguez, dean of Northwestern University's School of Law, says corporate sponsorships at the school "ended the moment Butler left." Rodriguez says the school recently decided to terminate the programs. The dean says he's against corporate sponsorship of judicial seminars.
"These programs should be free from any real or perceived conflict of interest," he says.
Butler spoke at more judicial conferences than any other instructor, records show. The professor and prominent conservative formerly of Northwestern is now executive director of George Mason's Law & Economics Center.
He has taught judicial seminar courses with titles like "Economic Thinking" and "Economics of Insurance." A former Republican candidate for Congress - he lost a 1992 bid - Butler was a "Koch Distinguished Professor of Law and Economics" at the University of Kansas.
Butler declined to be interviewed for this story. Daniel Polsby, dean of the George Mason University School of Law, also declined to answer questions, but did say: "We're very proud of the activities and programs of the Law & Economics Center" via email.
One frequent attendee of George Mason's judicial seminars, Judge Bennett of Alabama bankruptcy court, told the Center "I'm not going to be snowed by anybody's presentation." He said he finds the seminars "infinitely invaluable."
"You can accumulate information much more quickly than if you sit in your office and read stuff," he says.
John Dunbar contributed to this report.
The Center for Public Integrity is a non-profit, independent investigative news outlet. To read more on this issue, please visit publicintegrity.org.