Non-magnetic drill collar (NMDC) alloys are (Cr-Mn/Cr-Mn-Ni)-Mo-N proprietary austenitic stainless steels that meet minimum API Specification 7-1 requirements. Among NMDC alloys, a wide range of chemical compositions and environmental performance exist with similar mechanical requirements. NMDC alloy proprietary compositions may be grouped into premium and standard grades and, depending on the product and operation requirements, the drilling conditions may lean more towards one group versus the other. This paper evaluates and compares the corrosion performance of representative alloys from these two groups in terms of weight-loss corrosion, localized corrosion, and environmentally assisted cracking in two simulated drilling muds. The test program accounts for different levels of chlorides, dissolved oxygen, brine pH, and temperature, in order to reproduce corrosion in the environment(s) and temperature(s) representative of field jobs. This investigation aims to understand and identify corrosion and cracking limits of the alloys from the premium and standard groups; and consequently, provide guidance to improve operational reliability and increase NMDCs life in the field.