According to the forbes

If you were to ask Scotch whisky fans and collectors which distillery is amongst the most valued and in demand from collectors, you’re likely to hear Port Ellen as the one of the first names mentioned.

Though the Diageo-owned, Islay-based distillery last closed down in 1983, there was a few casks left over in its warehouses that were released as bottlings that became highly prized by collectors, with prices skyrocketing over the years as a result.

Read more at source: forbes