You need to look at the datasheet for the particular crystal you're aiming to use in order to find the recomended load capacitance. A Digikey search on crystals with 18pF load capacitance brings up ~4000 items so you should be able to find one that you can use with your capacitors.

If you already have the crystal (and no datasheet for it) then why not simply try it. It will most likely work but the frequency might be a bit off depending on how far from it's ideal load capacitance value you are - try it.