Certain substituted phenolic compounds when used with or without 1,2-epoxides as the sole stabilizer components are very effective in stabilizing n-propyl bromide (NPB). In a standard commercially important 60° C. stability test, representative substituted phenolic compounds used pursuant to this invention, can enable NPB to pass the test even though present at levels of about 50 ppm (wt/wt) or less in NPB containing no other stabilizer additive component. In fact, amounts as low as 1 ppm have been found effective with various substituted phenolic compounds. In addition, it has been found that one of the preferred stabilizers of this invention—2,6-di-tert-butyl-p-cresol—even though higher boiling than NPB, left inconsequential amounts of residue at least throughout the range of 1 to 30 ppm (wt/wt). Also, it has been found that certain other preferred stabilizers of this invention can provide synergistically improved stability in passing the 60° C. stability test when used with at least one 1,2-epoxide, notably butylene oxide.