Residential and commercial gas supplied across properties in Japan is categorized into two distinct types: city gas and propane gas, also known as liquefied petroleum gas. City gas consists primarily of natural gas delivered directly through underground pipeline networks managed by regional utilities like Tokyo Gas, making it more cost-effective and environmentally cleaner for urban consumers. In contrast, propane gas is delivered via physical gas cylinders installed outside buildings, which is common in rural or older suburban areas. Propane gas features a significantly higher heat energy density than city gas, but it generally incurs higher monthly utility costs. The two gas types also require different safety equipment, such as gas leak detectors placed at different heights due to gas density variations.