The oil leak was discovered on the afternoon of 22 April 2010 when a large oil slick began to spread at the former rig site.[41] The oil flowed for 87 days. BP originally estimated a flow rate of 1,000 to 5,000 bbl/d (160 to 790 m3/d). The Flow Rate Technical Group (FRTG) estimated the initial flow rate was 62,000 bbl/d (9,900 m3/d).[42][43][44] The total estimated volume of leaked oil approximated 4.9 Mbbl (210 million US gal; 780,000 m3) with plus or minus 10% uncertainty,[3] including oil that was collected,[45] making it the world's largest accidental spill.[7][46] BP challenged the higher figure, saying that the government overestimated the volume.