Abstract: The geochemistry of Lunnan crude is comprehensively studied.This paper presents that Lunnan crude primarily originates from the Cambrian-Lower Ordovician source rocks, combined with the structural development history, the source rock evolution history and oil gas distribution characteristics.So the Cambrian-Lower Ordovician strata should be taken as major source rocks for petroleum exploration in Tarim basin instead of pinning our hope on search for giant oilfield in Middle-Upper Ordovician strata as major source rocks in order to avoid the existed misdirection.

Key words: Tarim basin, Lunnan oilfield, geochemistry, source correlation, petroleum potential