You could use either oil. Chainsaw oil is basically a 30 SAE oil that has additives in it that make it work better for chainsaws. The biggest benefit to Bar & Chain oil is that it is made to stick to the bar and chain better. Regular motor oil will fling off of the end of your bar much more making a mess. This can be a real problem if you are working around concrete, brick or stone as the oil will stain the stone surfaces.
I hope this helps!
-Mark
na Review by Naomi
Told my husband years ago that if anybody ever made a chain saw that was absolutely idiot proof, I wanted one. My Christmas gift last year was the P540 and I love it!! I can cut trees, limbs, etc without having to wait for a long armed male to do the job.