A Usermade Expansion Pack or UXP for short is an expansion pack made by a single designer or design team containing a variety of content. By definition, a User-Expansion must contain both animals and objects. It must be released or partial content is released. Because of this definition, many users or Groups can claim to be making a UXP however, to be considered a true User Expansion, it must be released or partially available. A User Expansion normally contains graphics and images such as a box art.

Many UXPs have been made such as Paranoia!, ZooTycoon ABC AVES, ZooTycoon ABC REPTILIA, European Expeditions, Arabian Nights, Island Excursions, and Blue Planet. Radical Remake is considered a UXP by some, but its categorization is debatable. Originally its only true addition (rather than remakes) was the Mustang; however, since then AD have added biomes to RR and released the Mustang along with other animals and objects in their Complete Collection expansion.