Drive Orbs are pickups used to increase the Drive Gauge in Kingdom Hearts II and Kingdom Hearts II Final Mix. A small orb increases the guage by one, and the larger orbs increase it by 10. You can receive more if you have the ability Jackpot. They are also needed to level up Master Form. The small orbs are worth one Experience point, and a large orb is worth three.
Different kinds of Heartless can drop Drive Orbs, but Nobodies will never do so. This can make it slightly harder to level up Final Form, since Drive Orbs would sustain the form for a bit longer. In addition, this means that it is impossible to level up Master Form when fighting Nobodies.
Two areas in which most of the Heartless drop Drive Orbs are Beast's Castle and the Land of Dragons. The Land of Dragons also has many carts that release Drive Orbs when inflicted with a Fire spell or combo.
In Kingdom Hearts II Final Mix, there is a new area called the Cavern of Remembrance. Along the way through the cavern are little floating Orbs that are that when attacked drop many Drive Orbs and sometimes items. This is to indicate that you need to use either Drive Forms or certain abilities that you learn from Drive Forms. The floating orbs are colored differently to signify which Form.