<p>Interactions between soil carbon (C), microbes, and minerals drive stabilization and destabilization of soil organic carbon (SOC), and understanding these processes is central to constraining timescales of SOC persistence. Fluctuating soil redox conditions control both C cycling by microbes and the formation of mineral-organic associations. To examine these impacts, we tracked the partitioning of two C substrates with different mineral sorptive affinities and bioenergetic yields under fluctuating soil redox conditions to investigate how redox status modulates the outcomes of substrate-mineral, and substrate-microbial interactions. We performed a five-month soil incubation experiment using ¹³C-labeled oxalate and glucose under four soil redox regimes: persistently aerobic, intermittently aerobic&#xa0;(two treatments) and persistently anaerobic. We determined the partitioning of added substrates into respired carbon dioxide (CO₂) and soil C pools. We found that, on average, 7 times more added glucose C was retained as SOC compared to oxalate C under persistent or intermittently aerobic treatments, but there were no differences between glucose and oxalate retention under anaerobic conditions. On average, 3 times more oxalate C was retained as SOC under anaerobic compared to either persistent or intermittently aerobic treatments. Our results suggest that substrate bioenergetic yield is a key predictor of new soil C stabilization when oxygen is available, even if intermittently. When anaerobiosis is sustained, however, the high sorptive affinity of oxalate may promote direct mineral association by new C. This work highlights the importance of considering the molecular characteristics of simple, low molecular weight C substrates when investigating SOC dynamics.</p>