Which two contract types are the most common in government contracting?

The most common contract types in government contracting are typically fixed-price and cost-reimbursement contracts. Fixed-price contracts provide a set price for the contract deliverables, offering cost predictability for the government and incentivizing the contractor to control costs. Cost-reimbursement contracts, on the other hand, allow the contractor to be reimbursed for allowable expenses incurred while performing the contract, thus providing flexibility when the exact costs can't be determined at the outset. These two contract types are used widely because they can cater to a variety of project circumstances, balancing the government's need for accountability and budget control with the contractor's need for flexibility and adequate funding.

The other options include various contract types but do not align as closely with the most commonly used categories in government settings. For example, performance-based contracts focus on outcomes rather than inputs, and although they are used, they are not among the most prevalent. Similarly, time and materials contracts are beneficial for specific scenarios but do not have the broad application that fixed-price and cost-reimbursement contracts do. Indefinite delivery contracts are often used for recurring goods and services but are not a contract type themselves, as they can incorporate various forms of pricing structures.