A Chinese-born American geologist was released from prison in China after serving more than eight years on charges of procuring state secrets, a human rights group said Saturday.

Xue Feng returned to his family in Houston, Texas, on Friday after being deported immediately following his release, the San Francisco-based Dui Hua foundation said.

The foundation has long advocated on Xue's behalf, and Executive Director John Kamm said in a statement that he was relieved Xue was home after what he called a "terrible ordeal."

A staffer at Beijing's No. 2 Prison, where Duihua said Xue was held, said he wasn't authorized to release information to the media.

The 50-year-old Xue was detained in November of 2007, and sentenced in 2010 on charges of illegally gathering information on China's oil industry.

His case raised questions about whether normal business activities elsewhere might conflict with China's vague state security laws. Supporters also said Xue was physically abused in detention and denied proper legal rights.

Xue was born in China and earned a doctorate at the University of Chicago, where he was praised by his advisers for his thoroughness and hard work. After becoming a U.S. citizen, he returned to his native country to work for U.S. consultancy IHS Energy, now known as IHS Inc.

American diplomats had lobbied hard for Xue's release, saying his alleged crimes didn't warrant the harshness of his sentence.

In pronouncing him guilty, the Beijing No. 1 Intermediate People's Court said his actions "endangered our country's national security." The verdict said Xue received documents on geological conditions of onshore oil wells and a database that gave the coordinates of more than 30,000 oil and gas wells belonging to China National Petroleum Corp. and listed subsidiary PetroChina Ltd.