Higher ethanodiamondoids (ethanodiamantanes and ethanotriamantanes) have been identified for the first time in petroleum. Because ethanodiamondoids are the most thermally stable complex saturated hydrocarbons in petroleum, they appear to reflect the level of oil thermal stress and may serve as a promising reliable indicator for oil cracking and oil maturity. As the ethano-bridged diamond lattice molecules, the extraordinarily thermostable characteristics and predictable derivatizable features of ethanodiamondoids make them attractive components for nanomaterials and devices as well as heat-resistant materials.