The 2006-W Mint State $100 Platinum coin has one of the lowest mintages for the entire series. Not to mention, with the mintage of about 3,000 coins struck it is also one of the lowest mintage coins for any modern coin series.
In the year 2006, this was also the first time that the U.S. Mint produced an Uncirculated Platinum Eagle with a "W' mint mark. The coins were struck on special burnished planchets and sold to collectors at a premium over the spot price of platinum.