Credit default swaps are a crucial profit center for big banks. According to a report by Deloitte, the financial instruments account for roughly $55 billion of the banking industry’s annual revenue. So in 2009, when regulators began investigating alleged collusion by the banks controlling the CDS market, it seemed like plaintiffs lawyers would be clamoring for a piece of the action.

Four years later, the litigation offensive is finally taking shape, albeit more modestly than we expected. The complexity of the claims, the uncertainty of big payoffs, and the risk of taking on Wall Street behemoths may have kept most large institutional investors on the sidelines so far. But there’s no question that this will be a case to watch–and a big source of revenue for the banks’ army of lawyers.

It kicked off on May 3, when a coalition of plaintiffs firms led by Scott & Scott filed a class action against a dozen banks, including Bank of America Corp., Citibank Inc., and UBS AG. The complaint, filed in U.S. district court in Chicago on behalf of a Cleveland-based pension fund, alleges that the banks engaged in “egregious anticompetitive conduct,” like blocking CME Group Inc. from launching a first-of-its-kind CDS exchange and suppressing the release of real-time price data.

Eager to vie for lead counsel status, other plaintiffs firms have filed similar complaints in Chicago in the last two months. Berger & Montague, Cohen Milstein Sellers & Toll, and Korein Tillery jumped into the fray on July 11, filing a similar class action complaint on behalf of a group of Danish pension funds. The German pension fund LBBW Asset Management Investmentgesellschaft mbH and its lawyers at Motley Rice filed their own suit on July 29. Korein Tillery struck again that same day, this time on behalf the bankrupt brokerage firm MF Global, which both purchased CDS from the banks and sought (unsuccessfully) to become a clearing broker for swaps. MF Global alleges that its foray into the market was stymied by the banks.

The lawsuits seemingly got a boost on July 1, when the European Commission announced that it has preliminary concluded that 13 banks colluded to suppress competition in the CDS market between 2006 and 2009. A probe by the U.S. Department of Justice is still pending. Plaintiffs lawyers have so far relied primarily on the fruits of their own investigations, said Daniel Small of Cohen Milstein. “This issue has been on our firm’s radar for many months,” he said.

All told, four complaints have been filed in Chicago and one complaint has been filed in U.S. District court in Manhattan. Plaintiffs lawyers have urged the Judicial Panel on Multidistrict Litigation to funnel all the cases to federal court in Chicago. That’s where CME Group’s ill-fated exchange was based.

Five complaints is a relatively small number for an MDL against the banking industry, said Korein Tiller partner George Zelcs. “It’s certainly less than I’ve seen before in these sorts of cases,” he said. “It’s a very large and complicated case that’s going to require significant resources to ligate. Whether than translates into a barrier of entry, I don’t know.”

One of the Scott & Scott attorneys who filed the first complaint, Christopher Burke, told The Wall Street Journal that some investors are wary of joining the litigation, lest they anger the banks that control the credit markets. That could explain why a bankrupt entity like MFGlobal, which has little to lose, is the only large investor to jump into the fray so far.

In any case, the litigation is already generating billables for a bevy of defense-side firms. The line-up so far includes Skadden, Arps, Slate, Meagher & Flom (for JPMorgan Chase & Co.); Sullivan & Cromwell and Winston & Strawn (for Goldman Sachs & Co.); Sidley Austin (for Citigroup); Allen & Overy (for BNP Paribas); Davis, Polk & Wardwell (for Bank of America); Jones Day (for Deutsche Bank AG); Hogan Lovells (for Credit Suisse AG); and Mayer Brown (for HSBC Bank plc).