Creosote mixed with coal-tar creosote, or fortified with pentachlorophenol. Water-gas-tar creosote is also derived from petroleum oil or shale oil, but by a different process; its distilled during the production of water gas. The tar is a by-product resulting from enrichment of water gas with gases produced by thermal decomposition of petroleum. Of the creosotes derived from oil, it is practically the only one used for wood preservation. It has the same degree of solubility as coal-tar creosote and is easy to impregnate into wood. Like standard oil-tar creosote, it has a low amount of tar acids and tar bases, and
Coal Oil Point seep field of natural gas per barrel of petroleum. Leakage from the natural seeps near Platform Holly, the production platform for the South Ellwood Offshore oilfield, has decreased substantially, probably from the decrease in reservoir pressure due to the oil and gas produced at the platform. Written records, dating from as early as 1792, describe effects of offshore seeps in the Santa Barbara Channel. Oil and tar "slicks" have long been a trademark of the area. In 1792, Captain Cook's navigator George Vancouver recorded on passing through the channel: It had been commonly assumed that the local Chumash Native Americans used COP