Reverse Auction Bidding is a recently developed auction method. In this form of bidding process, the roles of the bidders and the owner are interchanged in terms of the form of the economic transaction. The owner's objective is to drive the unit rates down and the bidder's objective is to maintain an acceptable profit level. A study into Reverse Auction Bidding commenced at Texas A&M University in 2004 and continues to this time, with this the eighteenth study in the series. This study is the second multi-group study in the research. In this study, a multiple group comparison was made between different numbers of bidders, with Games One, Two and Three having three, four and ten bidders respectively. All participants were faculty and students from the Department of Construction Science. The critical requirement for the participants is that they should have no prior experience using the Reverse Auction Bidding system. The eighteen studies have concentrated on new players, with future studies planned for repeat participants. A number of the recent case studies have shown personality has an impact on the performance of the bidders. However, this work was not controlled for personality, as the research objective was to determine the impact of a different number of bidders in a game. The Keirsey Temperament Sorter test was completed by all participants so that the results could be understood in terms of personality impact on the level of return to each participant. The results showed the number of bidders has a significant impact on the individual returns confirming the earlier work on varying the number of bidders. An increase in the number of bidders was shown to lead to a more competitive economic environment, which given usual economic circumstances lead to a reduction in the number of firms interested in bidding, for the self-evident economic reasons. This work points to the need to investigate a bidding group size of five or six, which is likely to be the self-constrained upper limit in a real economic system. Some interesting observations on the personality types suggest that further work is required in this area.