<p>Methane (CH₄) is a powerful greenhouse gas and natural gas is a fossil fuel, giving the gas supply chain a high mitigation potential. Here we document a source of CH₄ that is a pre-electrification legacy but still present in many cities worldwide: gas streetlights. This study draws on historical analysis and scientific measurement to determine why gas streetlights persist and the consequences of that persistence for the mitigation of climate change. We documented 1,126 historic gaslights still in use in Cincinnati, Ohio. Cincinnati gaslights numbered up to 9,500 in the late 1800s, but the decline has slowed in recent decades. We found that gaslights remain due to cultural preferences that may be relevant to understanding current resistance to electrification of gas stoves and vehicles. Nearly all gaslights tested (<i>n</i> = 82) were emitting CH₄ (mean = 1.7&#xa0;g CH₄ hr^− 1), an order of magnitude higher than other gas appliances, such as stoves and hot water heaters. Gaslights also emit carbon monoxide, sometimes at hazardous levels close to the source. Gas streetlights in Cincinnati emit a larger proportion of CH₄ than most of the natural gas supply chain, at an average loss rate for all streetlights of 4.2%. Gaslights are good candidates for CH₄ emission mitigation and a potential case study for public education about natural gas and the benefits of electrification, because they are a highly visible symbol of the city. However, efforts to reduce CH₄ emissions will require an understanding of both the material and cultural factors impeding transitions.</p>