Abstract. It was predicted that preference factions within decision-making groups will have greater influence to the extent that faction member preferences are based on a common pool of decision-relevant information. Such factions are said to exhibit high informational commonality (IC). Four-person groups decided how much money to invest in each of two pharmaceutical companies developing new cholesterol-lowering drugs. Prior to discussion, information about these companies and drugs was distributed among members such that two would initially prefer investing in one company and two would initially prefer investing in the other company. Further, whereas half of the information held by members of one preference faction was held in common between them (high IC), almost none of the information held by those in the other faction was held in common between them (low IC). It was found that groups invested more money in a given company when that company was initially preferred by their high IC faction. Additionally, high IC factions exerted greater influence on members' private allocation preferences. These effects appear to have been due to the ability of members in the high IC factions to work together in a more coordinated manner to argue their position.