Diversified downstream energy company Delek US Holdings (DK) recently announced a $400 million increase in its share buyback authorization that takes the company’s total available mandate to$562 million.   A share buyback, also known as a stock repurchase, occurs when a company buys back its own shares from the marketplace. This practice reduces the number of outstanding shares, which can increase the value of remaining shares and boost earnings per share (EPS). Over recent decades, share buybacks have bec ...