It can be bought in the Store 5 times in a day. The first XP boost is bought for 30 Tibia Coins, the second one for 45 Tibia Coins, the third one for 90 Tibia Coins, the fourth one for 180 Tibia Coins and the fifth one for 360 Tibia Coins.
You can purchase a boost that increases the experience points your character gains from hunting by 50%. The boost lasts for 1 hour hunting time: similar to stamina, the duration of the XP Boost will only be reduced while you are hunting. In case your stamina falls under 14 hours, the boost will be paused.
Between two server saves, every character can purchase up to five XP Boosts. Note, however, that the price for the XP Boost increases with every purchase.
Note, as long as your character has an active XP Boost, no further XP Boost can be purchased.
In case another bonus is active, such as a double XP weekend or a voucher, the boost will be added to the other bonus (e.g. double XP weekend = 100% bonus + 50% XP boost = 150% XP bonus)