National Oilwell Varco Inc. (NYSE: NOV), the Houston-based oil and gas equipment giant, said in a statement Thursday it tapped Clay Williams to become president and COO, after he had served as executive vice president and CFO since 2005.<br />Prior to that role, Williams was vice president and CFO for Varco International Inc. from 2003 until it merged and became National Oilwell Varco in 2005. Williams was named Best CFO of a large public company this year by the Houston Business Journal, as well as Best Growth Manager in the news organization's Best CFO awards.<br />Williams will be replaced in the role of CFO by Jeremy Thigpen, who will serve as senior vice president and CFO. Before the new appointment, Thigpen had served as the company’s president of downhole pumping and solutions since 2007, and has served in several positions at the company for the past 15 years, the company statement said.<br />National Oilwell Varco was the 10th-largest public company in Houston by revenue in 2011, with $14.7 billion in revenue, up 20 percent from 2010, according to the HBJ’s annual list of the largest public companies in the region.