1996 Phillips Petroleum Company
1997 Oklahoma Natural Gas Company
1999 Oxley Petroleum
2000 Vintage Petroleum
Helmerich & Payne, Inc.
2001 Phillips Petroleum Company
Vintage Petroleum
2002 Williams Production Company
2003 Williams Production Company
2004 Cimarex Energy Company
2006 Unit Petroleum Company
2007 Newfield Exploration Mid-Continent, Inc.
2008 Cimarex Energy Company
Newfield Exploration
Mid-Continent, Inc.
2009 Williams Companies, Inc.
Newfield Exploration