The oil and gas (O&G) supply chain represents a substantial source of methane emissions, notably from the production, transport, and use of natural gas. The natural gas supply chain is commonly divided into production, midstream, and distribution sectors; this study considers only facilities in the midstream sector; a related paper discusses similar work in production. The midstream sector is commonly further divided into gathering and processing (G&P) and transmission and storage (T&S) segments. Midstream facilities are more complex, and often have larger structures and buildings, than production and distribution facilities.