U.S. oil output will decline in 2016 for the first time in eight years as producers slash spending, the Organization of the Petroleum Exporting Countries said Monday, while the producer group continues pumping at high levels . In its closely watched monthly oil market report, OPEC slashed its U.S. oil production forecast by 280,000 barrels a day next year, to 13.538 million barrels a day, a number that includes natural gas liquids. That would be about 60,000 barrels a day less than in 2015, the first decline since 2008. The finding is consistent with what the U.S. Energy Information Administration said last week, predicting that U.S. crude production would average about 8.9 million barrels a day in 2016, down from 9.2 million barrels a day in 2015. OPEC said lower oil prices were forcing U.S. oil producers to cut spending and causing their wells to deplete faster than expected. […]