One's a solvent and the other is a lubricant. Hoppes #9 is a good solvent with some preservative qualities; Rem oil is a lube, any lube will have some solvent qualities. I use either Hoppes #9 or Kano Kroil as a solvent. When it comes to protecting my guns I only use "Tetra Gun Oil". Some people think that it's a little expensive, but it works and a couple of extra dollars is worth it when it protects an expensive gun. An 8 ounce bottle cost me $8 right from the company, in the store a 1 ounce bottle will cost you $4.