When attempting to attack a swarm, can one simply attack the square (AC 5) the swarm occupies or must the attack be directed specifically at the swarm? The intent is to cover swarm creatures in oil. As they can co-exist with others in a square, is the square available to attack?

I have always ruled that with a swarm you can attack the square or squares they occupy.

Not sure if there is specific RAW to cover this.

Me neither, I'm not sure why anyone would target the swarm itself then. Unless of course it was a flying swarm.

When attempting to attack a swarm, can one simply attack the square (AC 5) the swarm occupies or must the attack be directed specifically at the swarm? The intent is to cover swarm creatures in oil.

By targeting the swarm, you have the potential to deal much more damage.

If you've prepared a flask of oil with a fuse (full-round action) it has a 50% chance of igniting successfully. On success, it works like alchemist's fire.

With alchemist's fire, if you target the swarm and hit, the swarm takes 1d6 points of fire damage and another 1d6 next round. (+50% effect)

If you target the grid intersection, then adjacent squares take 1 point of fire damage. (+50% which rounds down to 1)

If, instead of attacking with the oil using Throw Splash Weapon, you pour it on the ground, it only affects one square, and deals 1d3 fire damage for 2 rounds once lit. (+50% effect)

Oil: A pint of oil burns for 6 hours in a lantern or lamp. You can also use a flask of oil as a splash weapon. Use the rules for alchemist's fire (see Special Substances and Items on Table: Goods and Services), except that it takes a full-round action to prepare a flask with a fuse. Once it is thrown, there is a 50% chance of the flask igniting successfully.

You can pour a pint of oil on the ground to cover an area 5 feet square, provided that the surface is smooth. If lit, the oil burns for 2 rounds and deals 1d3 points of fire damage to each creature in the area.

Alchemist's Fire: You can throw a flask of alchemist's fire as a splash weapon. Treat this attack as a ranged touch attack with a range increment of 10 feet.

A direct hit deals 1d6 points of fire damage. Every creature within 5 feet of the point where the flask hits takes 1 point of fire damage from the splash. On the round following a direct hit, the target takes an additional 1d6 points of damage. If desired, the target can use a full-round action to attempt to extinguish the flames before taking this additional damage. Extinguishing the flames requires a DC 15 Reflex save. Rolling on the ground provides the target a +2 bonus on the save. Leaping into a lake or magically extinguishing the flames automatically smothers the fire.

-edit-

Grick's spot on.

That's how it works.

Ol' Nejj wrote:

When attempting to attack a swarm, can one simply attack the square (AC 5) the swarm occupies or must the attack be directed specifically at the swarm? The intent is to cover swarm creatures in oil.

By targeting the swarm, you have the potential to deal much more damage.

TEXT REMOVED BY OL'NEJJ

Grick thank you for this detailed response, it resolves the choice to attack swarm or square. However, I want to know if I can attack a square, with a ranged touch, that a swarm is occupying. Does the square have cover or concealment for example? This is the kind of thing I would like to figure out a RAW ruling for.

I want to know if I can attack a square, with a ranged touch, that a swarm is occupying.

No.

You can instead target a specific grid intersection. Treat this as a ranged attack against AC 5.

You can't target a grid intersection occupied by a creature, such as a Large or larger creature; in this case, you're aiming at the creature.

Does the square have cover or concealment for example?

Assuming you're talking about a large swarm (4 squares) the center intersection is blocked, but any of the outside intersections should be valid targets, and would only have cover if you're on the wrong side.