I've seen estimates that between 1 and 10% (rather a large range, eh) of all natural gas is lost as leakage. Maybe 15% in Russia (thanks Gazprom). As a greenhouse gas methane is over 20 times more potent than CO2 (The article says 24 x). Here's a guy with some ideas.
From the Vancouver Sun:
Researcher finds way to measure pollution from flares and venting
You can't regulate greenhouse gas emissions if you can't measure them, says Carleton University professor Matthew Johnson, who has discovered some new ways to measure what happens at pipeline leaks and gas flares at oil wells.
"If you're going to legislate a reduction, you have to be able to measure how that reduction occurred and that's a huge challenge," Johnson said Monday after presenting some new research to colleagues.
Johnson filed a provisional patent this year on his newest technique -- a combination of mathematical models and instruments -- for measuring methane leaks in pipelines. Kilo for kilo, methane is 25 times worse than carbon dioxide as a greenhouse gas, said Johnson, who is Carleton's research chair in energy and combustion-generated air emissions....MORE