Studies published in 2016 further indicated that methane leaks from U.S. oil and gas operations were significantly higher than previously estimated, as were U.S. methane emissions overall, which increased by more than 30 percent over a twelve year period. Most of this excess methane, which is responsible for 30-60 percent of the recent upsurge of global atmospheric methane, represents leaks from U.S. gas and oil operations.