Description: Traditional pension cost methods are based on the actuarial present value of future benefits [which is a mean value]. As a consequence, these cost methods are deficient because they cannot provide plan sponsors with certain valuable information such as the probability that the accumulation of a particular sequence of contributions will ultimately provide sufficient funds to pay benefits, or the size of fund needed to ensure that retirees' lifetime benefits are paid with a specified probability. In response to these deficiencies, a new family of cost methods, called a-percentile cost methods, is developed. These cost methods are based on the probability of adequately covering all participants' benefits. Expressions for the normal cost, the accrued liability and the gain are provided. From Transactions of Society of Actuaries 1993, Vol. 45.