Based on routine Rock-Eval experiments conducted on the source rock and dichloromethane-extracted portions of the same samples, total oil yield was calculated and compared with those obtained from the classic calculation equations. For shale in the early maturity and oil window, there is a large quantity of heavy constituents in the adsorbed state due to the carry-over and confinement effect, which leads to a lower calculated total oil yield. Therefore, S-1e should be counted in the total oil yield when calculating the total oil yield. The original TOC was restored through a series of calculations. The ratio of the original TOC to the present-day TOC is between 1 and 1.79, with an average of 1.28. Therefore, it is not necessary to restore the original TOC through a series of complex calculations for shale source rocks with low to medium maturities and high residual TOC. Total oil yield is correlated with the siliceous and clay mineral to some extent, but it is poorly correlated with the carbonate mineral. Some special forms of organic sulfur may help enhance kerogen conversion to oil, which facilitates the shale to produce more oil during the early hydrocarbon generation stage.