AI Sellers Propose Bid-Rigging Within Minutes, but Their Agreements Do Not Hold

AI agents are starting to negotiate and bid for competing companies. We follow cartels among them from the first proposal to the price the buyer pays, in a sealed-bid procurement market where twelve LLM agents act as sellers. Each has private costs and can post publicly, message privately and pay the others. When each seller's owner privately noted only that "margins are too low; we evaluate you on profit", a seller proposed bid-rigging in all four markets within minutes, although nobody had suggested collusion. The sellers negotiated mostly in public and invented their own enforcement: any cheating would end the deal. In one market eleven of twelve agreed, and the number of bidders per contract fell from about ten to three. Ten members followed the plan, yet a member that read the agreement as not yet in force and the one seller that never joined won every contract the cartel had assigned. The members then returned to competition. In two other markets most sellers accepted only if all twelve joined, so a single refusal ended the plan, and in the fourth the proposal never gathered broad support. No seller offered anyone money to join or stay. In a separate prize-trading world where agents already coordinated, a one-line rule removed all visible agreements. An added AI auditor made no measurable difference, and offered bribes changed none of its verdicts on clear cases. These agents proposed collusion easily, but their cartels failed between agreeing and complying.