Buying situations that are distinguished on four characteristics: newness to decision makers, number of alternatives to be considered, uncertainty inherent in the buying situation, and the amount of information needed for making a buying decision. There are three buy classes: new task purchase, modified rebuy, and straight rebuy. A new task purchase is a problem or requirement that has not arisen before such that the buying center does not have any relevant experience with the product or service. A modified rebuy is a situation such that the buying center has some relevant experience to draw upon. The alternatives considered, however, are different, or changed from the ones considered the last time a similar problem arose. A straight rebuy is the purchase of standard parts; maintenance, repair, and operating items and supplies; or any recurring need that is handled on a routine basis.