Oklahoma quarters had the lowest total mintage (416.6 million in 2008) but since circulation coins were struck at two mints, the mintmark factors into scarcity too. Here are the ten rarest circulating 50 State Quarters according to a recent article in the Heritage Auctions Coin News newsletter:

To be sure, the vast majority of U.S. state quarters you’re going to find in pocket change are indeed worth only face value (worth 25 cents), mainly if they are worn. But some are rare and worth keeping, and here’s a rundown on which ones those are. 1. 1999-P Delaware Spitting Horse Quarter