The Ouachita Mountains, a relatively untested, potential hydrocarbon province, contain a thick Paleozoic section of apparently favorable source beds, reservoir beds, and trap configurations. To estimate the thermal maturity of these strata, vitrinite reflectance was measured on 89 samples collected mostly from Carboniferous rocks from throughout the Ouachita outcrop area.

Thermal-maturity contours generally parallel structural grain in the western two-thirds of the Ouachitas. Reflectance values (in oil) range from < 0.5% in the frontal thrust belt to > 3.0% in the core area in Oklahoma, and from about 1.0% to > 3.0% in analogous positions in Arkansas. Older strata on upthrown sides of thrust faults are more thermally mature than younger strata on downthrown sides.

In the eastern one-third of the outcrop belt, thermal maturities are significantly higher (2.0-5.0% R_o), and thermal-maturity contours cut obliquely across structural grain. Strata on either side of thrust faults display identical levels of maturity.

In the western two-thirds of the Ouachitas, sedimentary and tectonic burial have been the major influences of thermal maturation, although a Mesozoic thermal overprint has increased levels of maturity in Arkansas. Throughout this area, strata are within the oil and wet-gas windows. The anomalous levels and patterns of thermal maturity in the eastern third of the Ouachitas are probably the result of a thermal overprint related to Mesozoic rifting and intrusive activity in the Mississippi embayment. This thermal overprint has elevated the maturity of strata in most of this area above the level of hydrocarbon preservation, although maturities within the dry-gas window are retained locally.