The volume of oil spilled by Royal Dutch/Shell's Nigerian unit fell more than 30 percent to 50,200 barrels in 1998 from 76,000 barrels the year before, the company said. In its annual report on the environment, Shell said the number of spills decreased slightly to 242 from 254 in 1997. Shell has been keen to promote its environmental record in Nigeria since coming under attack from campaigners in 1995 following the execution for murder of nine Ogoni activists who campaigned for autonomy and against pollution by oil firms.