Thomas L. Mitchellis joining Devon Energy Corp. as CFO and executive vice president. Incumbent financial chief Jeff Agosta is leaving to pursue other interests but it is "not related to any issues regarding financial disclosures, accounting matters or other business issues," the company said. Mitchell has been serving as CFO of Midstates Petroleum Co. From 2006-2011, he was CFO of Noble Corp. and for 18 years before that he worked for Apache Corp.