He is too old to be having "accidents." This is definately not a potty training issue. I would first rule out a medical condition. He may have a bladder infection or a urinary tract infection. Then rule out a major stress issue (recent move, new day care, death in the family, etc.)
If you learn he is doing it for attention or pressing limits, offering rewards will make it worse because that isn't positive reinforcement, it's bribery. He will learn that he can start misbehaving to get what he wants.
Consequences must be natural, related to the behavior, and unpleasant enough that it will stop. Once you have ruled out anything medical and you are sure he is doing it on purpose, I would sit down and calmly have a talk with him. This is his problem, not yours. So don't get upset or he wins. Tell him he gets one pair of pants per day. If he wets them, he has to wait until tomorrow to get a new pair. By the way, boys with wet pants can't sit in front of the TV or the computer or go out anywhere. And if he ruins his underwear, he will have to earn the money to buy new ones.
I saw a woman try this on Dr. Phil's recommendation and she had her kids wear a plastic bag to protect the furniture. Her son wet twice and stopped. Remember, this method is ONLY for fully potty trained children who are wetting or pooping intentionally for attention, to get out of time out, to manipulate parents, etc. It isn't appropriate for potty training accidents.