The overarching goal of the project is to measure the distribution of fugitive methane (CH4) emissions in the Marcellus Shale from public roadways with a unique trace gas sensing mobile laboratory, quantify uncertainties in emissions estimates from mobile measurements using dedicated micrometeorological case studies and modeling, and identify how various individual well metrics (total production, days since well completion) link to the distribution of emissions. The work will quantify CH4 emissions from 1000 individual gas/oil facilities (pads, wells, and associated infrastructure such as compressor stations, storage facilities) operating within the Marcellus Shale. A novel, multi-gas (CH4, C2H6, NH3, N2O, CO2, H2O, and CO) mobile environmental sensing laboratory equipped with fast and sensitive, laser-based sensors will help to distinguish between emissions from gas/oil extraction and other sources (landfills, agriculture, wetlands, combustion, etc.). Numerous (20) case studies will be conducted to quantify how emissions derived from the mobile laboratory data compare with those involving more data intensive micrometeorological measurements and modeling. Specific objectives of this study are: 1. Measure the distribution of fugitive CH4 emissions from ~ 1000 individual gas/oil facilities within the Marcellus shale play. 2. Quantify the extent to which mobile surveys can be used to identify the large emitters. 3. Develop guidelines for mobile sampling of plumes with associated uncertainties. 4. Examine the distribution of emissions versus production and history parameters (days since drilled, total production, operator).