The Environmental Protection Agency conducted a survey of 7,388 light-duty motor vehicles for tampering with emissions control devices. All vehicles inspected were classified into one of four mutually exclusive categories: tampered (at least one control device removed or rendered inoperative), arguable tampered (potential, but not clear tampering), malfunctioning, and ok (all control devices present and apparently operating properly). The results were: tampered 19%, arguably tampered 12%, malfunctioning 3% and ok 67%. The survey also found that 7% of the unleaded vehicles were subject to fuel switching (using leaded gasoline in vehicles requiring unleaded fuel).