The sector's routine oil discharges declined from 9,044 tonnes in 1993 to 6,632 in 1997. But the number of accidental spills increased from 183 to 346. Chemical discharges increased in the two years for which data are provided - 1996 and 1997 - but UKOOA says this was the result of a move away from oil-based drilling muds. It also says that discharges of the most damaging chemicals declined over the two years. The report also reveals that the industry accounts for 4% of the UK's CO2 and 2.5% of its methane emissions.