Wireline density measurements are highly valuable in mineral exploration and development. They are used in reserve estimation, ground stability analysis, seismic correlation, hardness mapping, and moisture analysis. Currently, wireline density is primarily measured in an open hole, using both legacy single-detector tools as well as modern compensated tools. However, in areas prone to hole collapse due to unstable ground conditions or in active mining areas, large portions of a resource may go unmeasured due to the potential of losing the tool (with radioactive source) when logging in the open hole environment. Whilst conventional logging tools can be adapted to provide an environmentally corrected density measurement through single wall drill rods (such as diamond drill rods) or casing (Ellis et al, 2004), it is considerably more complex to adapt existing open hole tools to measure inside Reverse Circulation (RC) drilling rods. Not only are the standard tools usually too large to fit in RC drill rods, but there are multiple rod types and combinations of fluid and air layers which affect the measurement. To address these complications, a new tool has been designed, along with processing methods to compensate for the complex in-RC rod environment. In this paper we discuss the development and field trials of a wireline density tool designed to operate inside RC drill rods. The methods used to compensate for RC rods, water levels, and tool position are described. Quality control techniques to ensure that the environmental corrections have been correctly applied are also suggested. The success of the tool has implications for the planning of resource definition programs as more data can be recovered in areas with unstable ground conditions, where the lost-in-hole risk associated with radioactive sources prohibits density tools being run in an open hole environment. CITATION: Market, J, Rossiter, H, Byrne, C, Enright, M and Armitage, B, 2019. In-RC rod density enabling data acquisition in unstable ground, in Proceedings Mining Geology 2019, pp 425434 (The Australasian Institute of Mining and Metallurgy: Melbourne).