Complex sentence: McMillan was the chairman and CEO of Permian Exploration Corporation, an oil exploration company, the chairman of the First Federal Savings Bank in Roswell, New Mexico, and the founder and CEO of McMillan Production Company.
Split into simpler sentences: McMillan was the chairman and CEO of Permian Exploration Corporation, an oil exploration company. He was also the chairman of the First Federal Savings Bank in Roswell, New Mexico and the founder and CEO of McMillan Production Company.