Chazen will replace Ray Irani, who will continue as full-time executive chairman, the company said in a statement.
Irani will retire in 2014.
Chazen joined Occidental in 1994 as an executive vice president. Five years later, he was named as chief financial officer. In August, he was made COO and elected to the company's' board of directors.
Before working for Occidental, Chazen was a managing director of Merrill Lynch's investment banking group.