Methane creares half as much CO2 per BTU of energy as gasoline. However methane its self is a greenhouse gas 20 times more potent than CO2. So if more than 2.5%

Methane creares half as much CO2 per BTU of energy as gasoline. However methane its self is a greenhouse gas 20 times more potent than CO2. So if more than 2.5% of methane leaks into the atmosphere, it cancels its relative cleanness. I dont think anyone knows how natural or idustrial leakage there is. But some groups are attempting measure.