Abstract: Penglai 19-3 Oilfield is the largest oilfield found in China^’s offshore area. Part of crude oil produced in this oilfield is immature and low-mature oil. A large quantity of experimental data about crude and source rock were used to systematically analyze the physical properties, group compositions and biomarker compounds of immature and low-mature oil from Penglai 19-3 Oilfield. The study is made on the sedimentary environment of source rock, characteristics of source rock and organic matter evolution. The results of the study indicate that immature and low-mature crude oil from Panglai 19-3 is characterized with high density, high viscosity, middle sulfur content, low wax content, low saturated hydrocarbon content, low saturation-aromatics ratio, high non-hydrocarbon content and high asphaltenes ratio, low Pr/Ph, low rearrangement sterane abundance and Ts