Until April, no woman had ever headed a major U.S. energy explorer. That changed when 35-year industry veteran Hollub landed the top spot at $12.5 billion Occidental. Less cheery: A mineral engineer by training, she ascends to the top as the worst oil bust in decades has gouged revenue and jobs in the industry (Occidental’s net sales sank 35% last year). Going forward, Hollub has vowed to put particular emphasis on development in and around the Permian Basin, the largest oilfield in the U.S. and a vital profit driver for the company.