A system for producing petroleum products from oil shale includes one or plural kiln lines made up of plural series-connected, indirect-fired, inclined rotary kilns. Plural kiln lines are operated for parallel processing. Oil shale is advanced through kilns in succession and exhausted from each kiln line substantially free of hydrocarbons. Successive kilns along the advancement of oil shale are maintained at successively higher temperatures. A fuel distinct from hydrocarbons in oil shale, such as syngas from a gasifier or hydrogen gas from a separator, drives pyrolysis to extract hydrocarbons. A refining unit located proximate to the kiln lines upgrades extracted hydrocarbons into petroleum products and separates the petroleum products by criteria. A heat extraction unit recovers heat from exhausted oil shale for reuse in kilns. A method involves drying oil shale followed by heating dry oil shale in successively hotter pyrolysis environments.