Ron Zacapa Rums are made from sugar cane harvested in southern Guatemala, which is pressed into virgin sugar cane honey, a process unique to the Guatemalan style of rum production. This liquid is then fermented, distilled and taken to the mountains for aging, where the flavor of the rums is further refined through the premium aging process known as Sistema Solera.
The Ron Zacapa Centenario XO is blended from these solera aged stocks which range in age from 6 years to 25 years. These stocks were aged in special cellars more than 7000 feet above sea level. The solera barrels are a mixture of reused American Bourbon, Sherry, Pedro Ximenez wines, and Cognac barrels. The combination of solera aging and the wide variety of reused barrels creates a highly complex rum with a rich aroma and flavour.
Here is a link to the review of the #20 spirit on my Rum Howler Top 100 Spirits Countdown of the best spirits I have ever tasted.
#20 – Ron Zacapa XO (25 Year Solero) Rum
________________________________________________________________
You may follow my Countdown list of the 100 Best Spirits here: The Rum Howler 2015 – Top 100 Spirits
Diplomatico Exclusiva Reserva is a premium rum which is produced from both column still rums and pot still rum. Within the blend are rums which are aged up to 12 years. The combination of tropical aging, batch still production yields an exquisite rum which has long been one of my favourites.
In November 2012 I revisited the Appleton 12 year Old Rum and found that my appreciation of the rum had increased substantially. Another visit to the bottle this year only reinforced that opinion. The Appleton 12 Year Old XO Rum has improved over the years (or perhaps my taste has).
I am not sure exactly what happened to Oliver and Oliver as current information about their company is very hard to find. However, the 
After distillation, the Zacapa rum is transported to the ‘House above the Clouds’ in the Guatemalan mountains for maturation. Special cellars age the rum at an altitude of more than 7000 feet above sea level where the ambient temperature is much more stable and the oxygen levels are lower than at lower elevations. The more stable ambient temperature ensures that the aging barrels are subject to less differential air pressure between the outside and the inside of the barrel.
The Rum Howler Blog 