In one post I suggested that legal departments, when they decide to send out an RFP, think like seniors who apply to college: three stretch firms that might be too costly for the work, three sure-fire firms that probably share the economics of the department, and three safeties that are lower cost.
Likewise, when you send out RFPs, nine law firms seems to be a good number of recipients. Support for my consultant’s sense of the right number comes from the Harvard Bus. Rev., Vol. 87, Dec. 2009 at 102. That article about whether to negotiate or conduct an auction says that “In many contexts, sellers consider the magic number of bidders to be somewhere between five and eight.” Elsewhere: “After about 15 bidders, auction theory estimates, the value of having an extra bidder becomes negligible – as long as the bidders are similarly situated.” Based upon this, invite about nine law firms capable of doing the work you have on offer.