Añejo ("aged") tequila is aged a minimum of one year, but less than three years in small oak barrels. Añejos are often rested in barrels that have been previously used to rest reposados. Many of the barrels were previously used for aging whiskey or bourbon, and Jack Daniels barrels are especially popular. This treatment creates many of the aspects of the dark color and more complex flavors of the añejo tequila. After aging of at least one year, the añejo can be removed from the wood barrels and placed in stainless steel tanks to reduce the amount of evaporation that can occur in the barrels.