Although “coal oil” was well known by industrial chemists at least as early as the 1700s as a byproduct of making coal gas and coal tar, it burned with a smoky flame that prevented its use for indoor illumination. In cities, much indoor illumination was provided by piped-in coal gas, but outside the cities, and for spot lighting within the cities, the lucrative market for fueling indoor lamps was supplied by whale oil, specifically that from sperm whales, which burned brighter and cleaner.[15]