Employing a sample set of 289 Thai listed firms during 2005-2014, the research found that leverage leads to increasing market power as measured by Tobin’s Q and sales growth. The explanation is given by the limited liability theory; that is, a firm employs debt as a commitment tool to compete aggressively in product markets. The main finding remained robust through different leveraged firms/groups, different market concentration groups, different time periods, and in different industrial sectors. Additionally, leverage had stronger effects ...