There are actually four spells in the conjure elemental spell.
The wizard is able to conjure an air, earth, fire, or water elemental with this spell - assuming he has the material component for the particular elemental. (A considerable fire source must be in range to conjure a fire elemental; a large amount of water must be available to conjure a water elemental.) Conjured elementals have 8 Hit Dice.
It is possible to conjure successive elementals of different types if the spellcaster has memorized two or more of these spells. The type of elemental to be conjured must be decided upon before memorizing the spell. Each type of elemental can be conjured only once per day.
The conjured elemental must be controlled by the wizard - the spellcaster must concentrate on the elemental doing his commands - or it turns on the wizard and attacks. The elemental will not break off a combat to do so, but it will avoid creatures while seeking its conjurer. If the wizard is wounded or grappled, his concentration is broken.
There is always a 5% chance that the elemental turns on its conjurer regardless of concentration. This check is made at the end of the second and each succeeding round.
An elemental that breaks free of its control can be dispelled by the caster, but the chance of success is only 50%. The elemental can be controlled up to 30 yards away per level of the spellcaster. The elemental remains until its form on this plane is destroyed due to damage or until the spell's duration expires.
Note that water elementals are destroyed if they are ever more than 60 yards from a large body of water.
The material component of the spell (besides the quantity of the element at hand) is a small amount of one of the following:
Air Elemental - burning incense
Earth Elemental - soft clay
Fire Elemental - sulphur and phosphorus
Water Elemental - water and sand
Special protection from uncontrolled elementals is available by means of a protection from evil spell.