The oil delivered to the reserve is "royalty-in-kind" oil—royalties owed to the U.S. government by operators who acquire leases on the federally owned Outer Continental Shelf in the Gulf of Mexico. These royalties were previously collected as cash, but in 1998 the government began testing the effectiveness of collecting royalties "in kind"—or in other words, acquiring the crude oil itself. This mechanism was adopted when refilling the SPR began, and once filling is completed, revenues from the sale of future royalties will be paid into the federal treasury.