United Airlines got the ball rolling last week with a new pact to plaster its name on the United Center for another two decades. But five other major sponsorship contracts are either expiring or up for bidding next year, a rare glut in a single market. All the sellers—the Chicago Bears, Chicago Bulls, Chicago Cubs, DePaul University and the village of Rosemont—are seeking high six- or seven-figure annual deals, setting up an array of options for businesses interested in making a splash in the local sports conversation. Experts are calling it a “perfect storm” that gives brands leverage by being able to comparison shop for sports investments that typically hit the market only every few years. The result has been a lengthier negotiating process that is forcing sellers to differentiate their offerings from local competition and prove companies' return on investment.