| g | Coefficient of skewness |
| GA | General Aviation |
| GABA | 4-Aminobutyrate |
| GABA A Receptor Binding | Gamma-Aminobutyric Acid Receptor Binding |
| GABA B Receptor Binding | Gamma-Amino Butyric Acid Type B Receptor Binding |
| GAC | Granular Activated Carbon |
| GAC Adsorption | Granular Activated Carbon Adsorption |
| GACT | Granular Activated Carbon Treatment |
| Gallon-RIN | Gallon-Renewable Identification Number |
| GAP | Good Agricultural Practice |
| Gasoline BOB | Gasoline Blendstock for Oxygenate Blending |
| GC | Gas Chromatography; General Counsel |
| GCG Separator | Gas-Condensate-Glycol Separator |
| GCM | General Circulation Model |
| GC-MS | Gas Chromatograph-Mass Spectrometer |
| GCWR | Gross Combination Weight Rating |
| GDF | Gasoline Dispensing Facility |
| GDP | Gross domestic product |
| GEE | Generalized Estimating Equation |
| GEM | Genetically Engineered Microorganism |
| GEM Model | Greenhouse Gas Emissions Model |
| GEN | Generation |
| GFAA Spectroscopy | Graphite Furnace Atomic Absorption Spectroscopy |
| GGBF Slag | Ground Granulated Blast Furnace Slag |
| GHG | Greenhouse Gas |
| GHG Auto Standards | Greenhouse Gas Auto Standards |
| GHG Inventory | Greenhouse Gas Inventory |
| GHG Performance Standard | Greenhouse Gas Performance Standard |
| GHG Registry | Greenhouse Gas Registry |
| GHGs | greenhouse gases |
| GI | Gastrointestinal |
| GIF | Graphics Interchange Format |
| GIS | Geographic Information System |
| Glass Manufacturing Metal HAP | Glass Manufacturing Metal Hazardous Air Pollutant |
| GLWQA | Great Lakes Water Quality Agreement |
| GM | Geometric Mean |
| GM EI | Groundwater Migration Environmental Indicator |
| GM Plant | Genetically Modified Plant |
| GMACS | Gas Manufacturer Alternative Certified Standard |
| GMIS | Gas Manufacturer's Intermediate Standard |
| GMO | Genetically Modified Organism; GRANTS MANAGEMENT OFFICE |
| GoF Test | goodness-of-fit test |
| GoF Test Method | Goodness-of-Fit Test Method |
| GOR | Gas-to-Oil Ratio |
| GOs | Grid openings |
| GPP | Green Purchasing Plan |
| GPR | ground penetrating radar |
| GPRA | Government Performance & Results Act |
| GPRA Measures | Government Performance & Results Act Measures |
| GPS | Global Positioning System |
| GPT | Glutamic-Pyruvic Transaminase |
| GRAS | Generally Recognized as Safe |
| GRS | GENERAL RECORDS SCHEDULE |
| GSA | General Services Administration |
| GSD | Geometric Standard Deviation |
| GSHP | Ground Source Heat Pump |
| GSSG | Oxidized Glutathione |
| GST | Glutathione-S-Transferase |
| GTAB | Gasoline Treated as Blendstock |
| GTBA | Gasoline-Grade tertiary Butyl Alcohol |
| GVW | Gross Vehicle Weight |
| GVWR | Gross Vehicle Weight Rating |
| GW | Ground Water |
| GWM | Ground Water Monitoring |
| GWP | Global Warming Potential |
| GWPs | Global Warming Potentials |
| GWUDI | Ground Water under Direct Influence |
| gy | Gray |