Understanding the failure mechanisms of resin-coated proppants under extreme environments facilitates the development of stronger proppants for superior long-term performance in the oil and gas sector. In the current study, the leaching behavior of Novolac resin-coated proppants (RCPs) and that of polyurethane (PU) based RCPs with aqueous media under different pH conditions and at elevated temperatures have been critically examined, to assess their chemical stability and integrity. Our study indicates that Novolac-based RCPs are substantially more stable to leaching conditions at 250 8F compared to PU-based RCPs. An in-depth nuclear magnetic resonance analysis of the aqueous leachates from the RCP systems reveals that the averaged total levels of the leached components from the PU-based RCPs is five-to sevenfold higher than those of the Novolac RCPs at the higher temperature. In addition, a critical examination of the Novolac RCPs from a product safety and environmental health viewpoint is accomplished by ultraviolet-visible spectrophotometric analysis of the aqueous leachates. The findings reveal that the concentrations of the phenolics, including free phenol, are lower than the detectable limits (<1 ppm) of the technique. V C 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45845.