Complex sentence: CBM production also involves release of methane into the atmosphere, often referred to as'fugitive' methane, and recent studies have found that fugitive release may be as high as 4 to 9% of the amount produced by a project.
Split into simpler sentences: CBM production also involves release of methane into the atmosphere, often referred to as fugitive methane. Recent studies have found that fugitive release may be as high as 4 to 9% of the total produced by a project.