The outlets in my basement are on a circuit with a 20 amp circuit breaker and 12/2 sheathed electrical cable wiring. However the outlets themselves are 15 amp and not 20 amp. Is this OK?

No, it's not OK. It doesn't meet code.

The receptacles are only rated for 15A, but the circuit breaker won't trip until over 20A.

But, in the real world:
- most electrical components are designed to handle roughly double their rating. So those can probably handle 25-30A before burning up.
- this only matters if you plug in something that draws more than 15A from this receptacle (or if you get a short in it). And that's a pretty big load -- things that draw that much usually are hard-wired, not plug-in.

This situation has been around in many houses, for many years, without problems. So it isn't an emergency that you need to fix immediately.

But do fix it. All you have to do is buy 20A receptacles (about $2-$3 each) and use them to replace the existing receptacles. That's probably only 10-15 minutes of work per outlet, even for a do-it-yourselfer.

As long as there is more than one receptacle on the circuit the code specifically allows 15 amp receptacles on 20 amp circuits.

And duplex receptacles count as 2.

From the 2005 NEC.

"210.21 Outlet Devices
Outlet devices shall have an ampere rating that is not less than the load to be served and shall comply with 210.21(A) and (B).
...
(B) Receptacles
...
(3) Receptacle Ratings Where connected to a branch circuit supplying two or more
receptacles or outlets, receptacle ratings shall conform to the values listed in Table
210.21(B)(3), or where larger than 50 amperes, the receptacle rating shall not be less than
the branch-circuit rating."

Now table 210.21(B)(3) will not copy and paste, but it shows

For 15 amp circuit not over 15 amp receptacle.

And for 20 amp circuit 15 or 20 amp receptacle.

This is not code, but commentary from the NEC Handbook.

"A single receptacle installed on an individual branch circuit must have an ampere
rating not less than that of the branch circuit. For example, a single receptacle on a 20-
ampere individual branch circuit must be rated at 20 amperes; however, two or more
15-ampere receptacles or duplex receptacles are permitted on a 20-ampere generalpurpose
branch circuit. This requirement does not apply to specific types of cord-andplug-
connected arc welders."

15 amp duplex receptacles are rated at 20 amps pass through in the UL listings. And each 1/2 of the duplex is rated at 15 amps. So they can handle a 15 and 5 or 10 and 10 amp loads for example.

And if you look closely at 15 amp GFCI you will see that they are also marked 20 amps feed through.

No matter how you read it , a 15 amp outlet is not allowed on a 20 amp circuit. A duplex does not count as two outlets!!! Understand the code instaed of reading into it!

15 amp receptacles are definitely allowed on a 20 amp circuit. Table 210.24 summarizes the requirements nicely. Table 210.21(B)(3) also shows that a 15 amp receptacle can be installed on a 20 amp circuit that serves 2 or more receptacles. Commentary following 210.21(B)(2) in the handbook clearly states that 15 amp receptacles are permitted on a 20 amp circuit.

Please cite a code section that prohibits 15 amp receptacles on a 20 amp circuit.