Disclosed herein are compositions including between 20 wt % and 50 wt % of a nitroxyl compound such as 2,2,6,6-tetramethylpiperidinyl-1-oxyl. The compositions are stable under field conditions of transportation and storage. The compositions remain homogeneous and pumpable or pourable at temperatures between −20° C. and 60° C., even when temperatures fluctuate in this range over a period of 10 days to 5 years, and even where the container used to transport and store the composition is made from metal or includes a metal surface contacting the composition.