Kim Lubel, CEO of CST Brands, is one of a small group of women who heads up a Fortune 500 company—there are only 21 female CEOs on the elite Fortune 500 list. And CST, the convenience-store chain, is ranked in the top 300 on that list with $10 billion in revenue.

Speaking with Fortune’s Susie Gharib at Fortune’s Most Powerful Women Summit, Lubel talked about her rise to the C-suite of the Texas-based company. Trained as a lawyer, most of the jobs Lubel held were on the legal side of the business as the lead attorney and negotiator in numerous merger deals. She confesses that becoming CEO was never a career goal. But when CST was spun off from energy giant Valero Energy, she was offered the CEO job, something she says “came by accident.”

Lubel shares some of the leadership lessons she’s learned in her three years as the head of CST and how she’s developed a natural leadership style. “I think at the core of all of it is being authentic and being who you are. And that’s just who I am,” she says. “So I think if you can keep your core piece there and be authentic wherever you are, you may have to modify the words you use and how you approach folks, but it’s still you.”