Bols Barrel Aged Genever is aged for a minimum of 18 months in French Limousin oak. It's a subtle difference from their young genever, but it imparts a nice maturity, smoothness, and light amber color.
Bols is probably the brand most responsible for bringing genever back into the consciousness of international drinkers, particularly in the States. As the cocktail revival took off, people searched out the famed "Holland gin" mentioned in books like Jerry Thomas' Bar-Tender's Guide. Bols delivered, reviving an old recipe that's smooth, fruity, and excellent either straight or in any number of classic cocktails (it can even replace whiskey in an Old-Fashioned—imagine that!).