A US 1845 10c St Louis postmaster's provisional cover could make in excess of $20,000 at Cherrystone Auctions.

It's cancelled by an 1846 circular date stamp.

The Charnley & Whelen correspondence is a famous set of St Louis provisional covers

The lot forms part of the famous correspondence (featuring St Louis Bear provisionals) that was sent to Philadelphia based firm Charnley & Whelen during the mid-1800s.

The St Louis Bears were printed in 1845-1846, prior to the introduction of the official US stamps in 1847.

They are so named for the depiction of the Great Seal of Missouri, which is supported by two bears, and are among the most desirable US provisional stamps available.

A rare single 20c made $85,000 at Robert A Siegel in 2013.

Other highlights include a 1979 $1 CIA invert - a very desirable modern stamp.

It's expected to sell for more than $14,000.

It was discovered by a CIA operative, who noticed the error on a pane of stamps at the agency's headquarters.

He convinced several colleagues to chip in on another pane and swapped it with the inverted stamps.

However, when the truth came out it caused a scandal and a number of the employees involved lost their jobs.

Cherrystone comments: "Because the number of existing CIA inverts approximately equals the number of existing Inverted Jennies…it may be said that current values... are far too low."

At present they regularly sell around the $15,000 mark.

The sale takes place on August 9.

Love stamps? Click here to look at what we have for sale.

Please sign up to our free newsletter to receive exciting news about postage stamp auctions.