ARIZONA: Billionaire investor Warren Buffett says a private gathering at an Arizona resort where Oprah likes to hang out was a great chance for the American billionaires who have pledged to give away at least half their wealth to meet each other, compare notes, eat and laugh. Buffett knew only about 12 of the 61 people at a Thursday dinner before the famously gregarious Berkshire Hathaway CEO worked the room and made 40 new friends. “They all more than fulfilled my expectations,” Buffett said Friday in a telephone interview. The media was banned from the first annual meeting of the group that has accepted the giving challenge by Buffett and his friend Microsoft co-founder Bill Gates. So were extended family, advisers, secretaries and the CEOs of the foundations represented by the billionaires at the Miraval Resort in Tucson. Since last June, 69 individuals or couples have made the giving pledge. Melinda Gates, cochair of the Bill and Melinda Gates Foundation, said she was delighted by the openness of the virtual strangers. At one point, conversation at her table drifted toward the biggest mistakes people had ever made as philanthropists. “One of the things about being a philanthropist, in many ways it's rather a lonely job,” said Tashia Morgridge, a retired special education teacher. She works with her husband, Cisco Systems chairman John Morgridge, to give money to improve US education through the Denver-based Morgridge Family Foundation. George Kaiser, a Tulsa, Oklahoma philanthropist who aids early childhood education and social services programs, said the giving pledge helps philanthropists who don't want to just throw money at causes and instead want to explore the best ways to invest money to tackle the world's biggest problems. “Being able to share with other people who are agonizing about the same decisions is extraordinarily useful,” said Kaiser, chairman of BOK Financial Corp.who has been an oil and gas industry executive for four decades. He led a session on applying analytical business practices to philanthropy. The goals of the organization do not include working together to pool philanthropic dollars. Still, the meeting in Tucson that ended Friday included sessions where different philanthropists shared their passion to improve education, the environment and other causes.