Basic Differences Between City Gas (Natural Gas) and Propane Gas (LP Gas)

・Composition and Properties

City gas is natural gas, primarily composed of methane, while propane gas is a liquefied gas mainly composed of propane and butane. Both gases are originally colorless and odorless, but an odorant is added for safety to help detect leaks.
 

The two gases also differ in weight. City gas is lighter than air, so if it leaks, it rises and spreads upwards. Therefore, gas leak detectors for city gas are generally installed near the ceiling. Propane gas, on the other hand, is heavier than air and will accumulate near the floor in case of a leak, so detectors for propane gas are installed close to the floor.

・Supply Method and Coverage Area

City gas is supplied to households through underground pipelines. Since laying these pipelines involves enormous costs, city gas is mainly available only in densely populated areas where the infrastructure can be cost-effective.
 

In contrast, propane gas is delivered in cylinders directly to homes, which allows it to be supplied even in regions without gas pipelines. While city gas is mostly limited to urban areas, propane gas can be supplied throughout almost all of Japan.

・Cost

Propane gas is said to be about twice as expensive as city gas. The higher cost of propane gas is largely due to the delivery process, as gas companies must transport heavy cylinders to each home, adding transportation and labor costs to the price. While city gas requires the initial investment of laying pipelines, once installed, the gas is supplied automatically through the network.
 

In addition, propane gas has always been under a free-pricing system, long before city gas deregulation. Gas companies have been able to set their own prices, and in some cases, unrelated equipment costs were added to the gas bills. To address these issues, from April 2025, it became mandatory for gas companies to provide a detailed breakdown of their gas charges.