Extensive, thick, and heterogeneous lacustrine shales occur globally with some regarded as source rocks, but which facies are the key contributors remains unclear. Previous studies have considered that all of the heterogeneous shales were source rocks in the Dongpu depression, but exploration does not support this assumption. Based on 40 yr of geochemical data collection, this study investigated the hydrocarbon generation and expulsion potential of these shales. The results show that laminated shales, though relatively limited in thickness and area, contain much higher organic matter contents and more oil-prone organic matter. Thermal simulation analysis shows that hydrocarbon generation and expulsion potential of laminated shales are much higher and more favorable for hydrocarbon expulsion. Oil-source correlation analyses between oil and shales indicate that northern oils feature pristane/phytane ratios (Pr/Ph) less than 0.7, gammacerane (gammacerane/C30-hopane) indices greater than 0.5, and L-shaped distributions of ααα-C27-20R, ααα-C28-20R, and ααα-C29-20R regular steranes, and are similar to the biomarker characteristics of northern laminated shales with total organic carbon (TOC) contents greater than 1 wt. %. In contrast, northern massive shales are characterized by a high Pr/Ph and low gammacerane index. Southern oils feature Pr/Ph greater than 0.7, gammacerane indices less than 0.5, and L-shaped distributions of regular steranes that are similar to the biomarker characteristics of southern laminated shales. Southern massive shales were characterized by high Pr/Ph, low gammacerane indices, and reversed L- and V-shaped distributions. Laminated shales with TOC contents greater than 1 wt. % are the key source rocks in these heterogeneous Paleogene shales.