A project manager would like to add external engineers to the current team.

A time and materials (T & M) contract is the best fit when you need temporary, specialized resources for a limited period (here, only during the testing phase) and the exact effort/hours are not fully predictable. With T & M, the buyer pays for the actual labor time (often at an agreed hourly/daily rate) and any approved materials/expenses. This aligns to CompTIA Project+ procurement objectives around selecting appropriate contract considerations and types, where time and material is a standard option used when work is phase-specific or scope is not fully defined to a fixed deliverable.

By contrast, fixed-price is most appropriate when the scope and deliverables are clearly defined upfront (less suitable for staff augmentation). Cost-plus reimburses allowable costs plus a fee and is typically used for broader, less-defined deliverables—often creating higher buyer cost risk than T & M for a small, contained staffing need. A warranty is not a primary contract type for acquiring temporary engineers; it’s usually a contract provision related to quality/defects after delivery.