The following information is from my eBook on Type One Liberty Head Double Eagles at http://doubleeaglebook.com/
The mintage figure for the 1851-O is nearly twice as great as the next most common double eagle from New Orleans (the 1852-O has a mintage of 190,000). The 1851-O is easily the most available New Orleans double eagle. It is plentiful in Very Fine and Extremely Fine grades, and can even be found in reasonably appealing About Uncirculated-50 to About Uncirculated-53 without a huge effort. It becomes very scarce in properly graded About Uncirculated-58, and it is very rare in Uncirculated with nearly all the known examples in the Mint State-60 to Mint State-61 range.
STRIKE: The strike seen on this issue is much sharper than on the 1850-O and it is among the best found on any double eagle from this mint. The obverse is usually well detailed with some of the hair strands showing individual definition The stars are likely to show weakness on the radial lines, although a few are found with full or nearly full stars on the obverse. The reverse is generally well struck with the exception of the tops of some of the lettering which is sometimes weak.
SURFACES: This is an issue which is generally seen with very heavily abraded surfaces. It is very hard (although not impossible) to find examples with relatively clean fields, especially on the obverse. Some higher grade 1851-O double eagles have swirls of either die polish or rust in the obverse fields and below the top lettering on the reverse. A few have been seen with black grease stains which are mint-made. It is possible to locate an example with choice surfaces but such coins are very hard to locate.
LUSTER: The luster on the 1851-O tends to be among the best seen on any Type One double eagle from New Orleans. High grade pieces show frosty luster or, less often, they are slightly reflective. I have seen around a half dozen which are prooflike and these can be quite spectacular in appearance. On a number of coins in the AU50 to AU55 range, the luster is impaired on account of excessive abrasions. And many have been cleaned, which causes the luster to be impaired.
COLORATION: The natural coloration is a pleasing medium green-gold hue. A few 1851-O double eagles have a rich lemon-gold color. Some have really nice original color, but such coins have become very hard to locate as so many have been cleaned or dipped in an attempt to get them into a higher grade holder.
EYE APPEAL: It is easier to find a nice 1851-O than any other double eagle from New Orleans. Many are well struck and have good luster. However, it is hard to find an example with very clean surfaces and which is original in appearance. Generally, very choice examples sell for strong premiums and 1851-O double eagles with CAC approval are bringing strong premiums when offered for sale.
INTERESTING VARIETIES: 1851-O double eagles are found with a heavy date and a light date. Positional varieties of the mintmark exist as well. None are of interest to collectors.
PROOFS:No Proofs were struck this year.
HOARDS: 14 examples were recovered from the S. S. Republic while another seven were recovered from the S.S. Central America. At least 10 were found in the Baltimore Hoard.
BUYING TIPS: Nice 1851-O double eagles tend to be of interest to type collectors seeking a single choice example to represent the Type One design. This means that there is good competition for attractive pieces. As this is likely to be the highest grade New Orleans double eagle in a collector’s date set, I suggest being patient and waiting for the right coin: one with minimal marks, a good strike, nice color, and real eye appeal.
AUCTION RECORD: The auction record for this date is $64,625, which was set by Stack’s Bowers 2/14: 2164, which grades MS62 by PCGS.
FINEST KNOWN: There are around four or five properly graded MS62’s known for this issue, and a few are choice for the grade. The two which stand out to me are the Crawford coin (probably ex Stack’s 1/84: 835, Amon Carter collection), and a coin I sold to a New England collector which is ex Heritage 2006 ANA: 5576 ($48,875). NGC has graded one coin in MS63 which I haven’t seen in its current holder; it is almost certainly a coin which was upgraded from an MS62 holder.
TOTAL KNOWN: 1500-2000+
Very Fine: 440-545
Extremely Fine: 645-855
About Uncirculated: 400-580
POPULATION FIGURES: As of the beginning of 2015, PCGS had graded one in MS60, one in MS61, and eight in MS62 for a total of 10 in Uncirculated. NGC had graded five in MS60, seven in MS61, six in MS62, and one in MS63 for a total of 19 in Uncirculated. These numbers are slightly inflated by resubmissions, especially in MS61 and MS62. CAC has approved just one coin in MS60 and another in MS62.
PERFORMANCE SINCE 2002: A Choice Extremely Fine example (equivalent to EF45) was priced at around $1,500-2,000 in 2002. Today, such a coin is priced at $5,000 to $6,000, and it is probably less choice than the 2002 version. A nice About Uncirculated example (equivalent to AU55) was priced at around $3,000-4,000+ in 2002. Today, such a coin is priced at $10,000-12,000 and, again, it is likely to not be as nice as the coin sold as “AU55” a decade ago.
COMMENTS: In my experience, the 1851-O double eagle is scarcer in high grades (About Uncirculated-55 and above) than the 1852-O. Some of the 1851-O double eagles which I have seen graded MS60 to MS61 by PCGS and NGC are questionable as to whether they are really “new,” and strictly graded Uncirculated coins remain very rare. Between the first edition of this book in 2002 and the current edition I revised my estimate of Uncirculated 1851-O double eagles from 10-15 to 15-20 (largely based on the fact that the combined PCGS/NGC population is 29 as of August 2014), but I am not totally convinced that this estimate is as generous as I have indicated.
David Akers (1975/88):
No O-Mint Double Eagle can be reasonably called "common" but the 1851-O is certainly the most often available of the 13 issues from this Mint. The majority of known pieces grade VF or EF but it is not especially unusual to locate a very nice AU. However, in full mint state the story changes dramatically and a true Unc. 1851-O is certainly rare. Choice or gem uncs are extremely rare and probably no more than a handful of such pieces exist. Virtually all known examples of this date are semi-prooflike or prooflike.