Google Inc.’s chief financial officer will retire by the end of the year, creating the most prominent job opening at the Internet search leader since it went public three years ago.

George Reyes’ departure as CFO, announced Tuesday, was unexpected - a development likely to stir speculation about his reasons for leaving a crucial job at one of the world’s most scrutinized companies.

Mountain View-based Google didn’t explain why Reyes, the company’s CFO since 2002, decided to retire at the age of 53. A Google spokesman declined a request to interview Reyes, who intends to remain on the job while he helps the company find his successor. The transition is expected to be completed before January.