Whole-rock analyses by x-ray powder diffraction and Rock-Eval pyrolysis studies were carried out on the Cenomanian/Turonian Derekoy formation shales from four sample sites in the Lower Antalya Nappe in the western Taurus region (SW Turkey) to determine rock-forming mineral assemblages, their abundance in bulk composition, and clay matrix effect on hydrocarbon yield during Rock-Eval pyrolysis. These studies indicate that the rock-forming minerals are mostly quartz (3-68%), clay minerals (32-81%) including smectite and illite, and rare to common calcite (0-39%), feldspar (0-5%) and mica (0-11%). High total organic carbon (TOC) contents (up to 42 wt%) and corrected hydrogen indices between 538 and 642 (mg HC/g TOC) correspond to marine organic matter (Type II kerogen) and excellent oil-prone hydrocarbon source rocks. Strong positive correlation (R-2 = 0.84 to 0.96) between hydrocarbon yield (S-2) and TOC content implies that the positive values of x and y -intercepts are relatively high, with values ranging between 1-13.117 mg pyrolysable hydrocarbon in 1 g of rock. These results mean that the clay matrix is the main agent of adsorbtion, and high amounts of hydrocarbon retention must be present.