A human rights group says American geologist Xue Feng has been released after serving more than eight years in a Chinese prison on charges of procuring state secrets.

The San Francisco-based Dui Hua foundation says Xue Feng returned to his family in Houston, Texas, on Friday.

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.

Xue was born in China and earned a doctorate at the University of Chicago. 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.