Alex O'Brien (born March 7, 1970 in Amarillo, Texas) is a professional tennis player from the United States, who competes on the ATP Tour. He was the No. 1 doubles player in the world (gaining that ranking on May 8, 2000) and was ranked as high as 30 in the world in singles (gaining that ranking on June 21, 1997).
He won his only singles title at New Haven, Connecticut, in 1996. He won 13 doubles titles, the biggest coming at the U.S. Open in 1999, the Cincinnati Masters in 1994 (his first doubles title), the Indian Wells Masters in 2000, and the Paris Masters in 1999.
He also reached 20 doubles finals, including the Australian Open in 1996 & 1997, the U.S. Open in 1995, the Miami Masters in 1998, and the Canada Masters and the Rome Masters in 1997.
He also played on the United States Davis Cup team, and was a four-time All-American at Stanford University where he won NCAA singles, doubles and team titles in 1992. He earned a bachelor's degree in American Studies at Stanford in 1992.