Oil firms trying to sell aging North Sea oilfields are considering shouldering hundreds of millions of dollars in future dismantling costs to help find buyers, industry sources say. One of the world’s oldest and most important offshore oil and gas production basins, the UK North Sea faces dwindling output and a growing number of redundant platforms that require decommissioning in a scale and complexity never seen before. The near halving of oil prices over the past year to below $60 a barrel has forced the industry to slash spending, increase efficiencies and sell or shut down assets that are least profitable or which do not fit their portfolios. But despite a large rise in the number of assets up for sale in the North Sea in recent months, only a few deals have been completed.