Forbes has an article that accounts for Natural Gas through its life cycle, not just in consumption.
One calculation that has stirred debate is that the natural gas number is as high as 1200 gCO2/kWhr.
However, new studies by Robert Howarth and associates at Cornell University (GHG Footprint of Natural Gas; National Climate Assessment; thanks to atomikrabbit for pointing me in this direction) provide emissions data from the entire natural gas life-cycle. Their results bump this number for gas from 600 gCO2/kWhr to over 1,200 gCO2/kWhr, making natural gas the largest emitter of GHGs in electricity generation. On the other hand, Howarth and company have been challenged by others that say their numbers are too high (BusinessWeek), particularly Lawrence M. Cathles, also of Cornell. Cathles contends that gas is still better than coal with respect to global warming. Even if Cathles is correct and 600 gCO2/kWhr is still the number for gas, it’s not that much better than coal compared to ther energy sources like hydro and nuclear.
For those of you have just switched to a power generation mix that has more natural gas than coal, you may be stuck again. And, your carbon footprint may be much bigger than you thought.