Houston, TX-based Par Petroleum Corp. has made three key management appointments.

Maurice Eaton has left his position on the board of directors for Northern Petroleum Plc (AIM:NOP) and various other operating subsidiaries.

Dennis de Vreede will join DeepOcean Group Holding BV as its CFO on August 1, 2013.

Pardee Resources Co. (PRC) has named Thomas A. Lopus as senior vice president, oil and gas. Pardee Resources is a Philadelphia-based firm that focuses on the acquisition, management, and responsible development of natural resource properties.

Energy and power-focused private investment firm Riverstone Holdings LLC has added former Anadarko Petroleum Co. executive James T. Hackett to the firm as a partner and co-head of the Houston office.

Clarence P. Cazalot, Jr., chairman, president and CEO of Marathon Oil Corp. (NYSE: MRO) has elected to retire on Dec. 31, 2013, after almost 14 years leading Marathon Oil and 41 years in the oil and gas industry. Cazalot will continue as executive chairman through Dec. 31, 2013.

Lloyd’s Register has appointed Chris Finlayson, chief executive of BG Group plc, and Ellis Armstrong, ex-CFO of E&P at BP plc, as non-executive directors on the board of Lloyd’s Register Group Ltd.

Tudor, Pickering, Holt & Co. (TPH) has hired Scott W. Archer as managing director in investment banking. Archer will specialize in midstream and MLPs at the energy investment banking firm.

EnerJex Resources Inc., a domestic onshore oil company with assets located in Eastern Kansas and South Texas, has appointed Richard Menchaca to its board of directors. Additionally, he has been elected to serve on the company’s Audit Committee.