Hi Bob,
"Oil" pastels are what I would describe as similar to soft crayons. They have a waxy carrier and when you draw on paper with them, they have a "slippery" feel and leave a line similar to, well, crayons. If you try to scrape a little off a stick, you may find that it sticks to your knife blade or comes off in flakes.
"Soft" pastels are like sticks of fine-grained chalk and do not have a waxy carrier. When you draw on paper with these, you should get a dry dusty appearance. If you scrape these with your knife, it should come off as a fine powder.
Sorry if this sounds vague, I haven't used oil pastels since school (over 35 years).