According to the PMBOK® Guide and the Standard for Procurement Management, the selection of a contract type is determined by the nature of the work, the degree of risk, and how well the scope is defined.

Time and Materials (TandM) contracts are a hybrid type of contractual arrangement that contains aspects of both cost-reimbursable and fixed-price contracts. They are frequently used for technical experts, consultants, or professional services when the specific scope of work cannot be quickly prescribed at the time of the agreement. Since a consultation fee is typically based on the expert ' s time spent and their specific hourly or daily rate, TandM is the most appropriate fit. It allows for flexibility when the precise number of hours required to reach a solution is unknown.

Fixed Price Incentive Fee (FPIF) is used when the scope is very well defined and the buyer wants to provide a financial incentive for meeting specific metrics (like cost or schedule). It is rarely used for simple expert consultations due to the administrative complexity of the incentive calculations.

Cost Plus Incentive Fee (CPIF) and Cost Plus Award Fee (CPAF) are cost-reimbursable contracts used primarily in large-scale, high-risk projects (like RandD or complex construction) where the buyer assumes the cost risk. These require a sophisticated accounting system to track every cost incurred by the seller, which is over-engineered and impractical for paying a simple consultation fee.

As per the PMI standards, when the requirement is for " staff augmentation " or " expert acquisition " where the duration is uncertain, Time and Materials is the industry-standard choice.