Which of the following is not a competitive procedure available for full and open competition?

Direct negotiation is not considered a competitive procedure available for full and open competition. In the context of federal contracting, full and open competition requires that all qualified vendors have a fair opportunity to compete for contracts, ensuring transparency and fairness in the procurement process.

In contrast, the other methods listed—combination of competitive procedures, sealed bids, and competitive proposals—are all designed to foster competition among bidders. Sealed bids involve solicitations where bids are submitted in sealed envelopes, ensuring that they remain confidential until the designated opening time, allowing for a clear comparison of offers. Competitive proposals involve a solicitation process where multiple vendors submit proposals that are evaluated based on criteria set forth in the request for proposals, thus encouraging a competitive environment.

The combination of competitive procedures refers to the use of different methods to enhance competition, such as using both sealed bids and competitive proposals for a single contract. These practices are rooted in the principles of fair competition and seek to maximize value for the government.

In summary, while the other options encourage competition and provide structured methods for evaluating bids and proposals, direct negotiation does not inherently meet the criteria for competitive procedures as it may not allow for multiple vendors to participate on an equal footing.