Complex organic molecules (COMs) are commonly observed towards star-forming regions and are of particular interest to origins of life studies due to their potential role as prebiotic molecule building blocks. Constraining COM formation pathways that operate at low temperatures (~10K) is critical both for explaining the detections of COMs towards prestellar sources and for predicting the efficiency of COM synthesis in planet-forming disk midplanes. We have performed a suite of laboratory experiments characterizing the viability of ice-phase oxygen atom insertion into hydrocarbons as a low-temperature COM formation pathway. We find that these insertion reactions are barrierless and proceed efficiently at 10K, so this process should readily occur under ISM conditions. I will discuss the energetics and product channels observed in our experiments, and the astrophysical implications for this chemistry. Oxygen insertion chemistry offers a novel path to molecular complexity on very cold grains where COM formation may otherwise be inefficient.