my oatmeal stout

Not an issue, that's not that much of a difference. All that's important is that it tastes good.

 

Depends on a lot of factors, but it may be done. (Most likely it is.) But whether 1.018 is probably done or not depends on a few things...

What was your measured (not expected) post boil OG?
What was the grain bill?
What yeast strain?

 

That's 70% attenuation, and you have a pretty significant amount of Crystal/Roasted malts. Could very well be done. I'd wait 3 days and check SG again. If it hasn't move, it's probably done. Then I'd wait a few more days and bottle.

 

Plus he mashed at 155F. I'd say it's done...

 

Unless you are in a huge hurry to drink this, I would follow Vikeman's advice above. Wait 3-4 days and check the gravity and then wait another 3-4 days to be safe before bottling. Or just leave it alone for a couple more weeks and bottle then. It's probably done now, but why risk bombs?

 

Actually, my advice to wait a few extra days wasn't to avoid bottle bombs (though that's a potential benefit too). It was to let the yeast clean up their byproducts.

 

Good advice. All my beers sit in primary for an additional 1-2 weeks after primary is 'done'. Lately I have been also cold crashing before I keg but I haven't always done that.

 

Sounds great, send one over this way.

 

I agree with this, but then why say "check the gravity and if it doesn't move..."? That sounds an awful lot like there is more for the yeast to do than clean up byproducts.

For the OP, my beers seem to be best with 3-4 weeks in the primary or at least 2 weeks in the primary and then a long secondary in the keg. There is a lot of benefits to leaving your beer alone for another week at least.

 

Yeah, it sounded like you thought the gravity might drop some more, hence my comment about bombs. I think we are in agreement here about the benefits of the OP leaving it alone for a bit. I could have saved us some typing by adding something about "cleanup" at the end of my original comment.