The Mobil companies were merged into and became subsidiaries of ExxonMobil , the world 's largest publically traded international oil and gas company in November 1999 . � � � � � � � � � � � � � � The Minerals Management Service ( MMS ) of the U.S. Department of the Interior is responsible for overseeing the collection of royalties on federal and American Indian leases , as well as federal offshore lands on the Outer Continental Shelf . � � Each month , companies are required to report to MMS the value of the natural gas produced from their federal and American Indian leases and to pay a percentage of the reported value as royalties . � � The United States alleged that the Mobil companies used transactions with affiliated entities to falsely reduce the reported value of gas taken from federal and American Indian leases , to claim excessive deductions for the cost of transporting that gas , and to otherwise understate the value they reported each month for their natural gas production .