A ProPublica review of U.S. Department of Labor investigations shows that oil and gas workers - men and women often performing high-risk jobs - are routinely being underpaid, and the companies hiring them often are using accounting techniques to deny workers benefits such as medical leave or unemployment insurance. The DOL investigations have centered on what is known as worker "misclassification," an accounting gambit whereby companies treat full time employees as independent contractors paid hourly wages, and then fail to make good on their obligations.