We test several claims about the relationship between unanimity rule and Pareto optimality. Buchanan and Tullock (1962), Mueller (2003), and other scholars argue that unanimity rule is more capable of producing Pareto optimal outcomes than other voting rules, such as majority rule, because unanimity rule passes an alternative only if it makes everyone better off. Majority rule can pass alternatives that make some individuals worse off. Dougherty and Edward (2008), in contrast, claim that majority rule is at least as likely to select Pareto optimal outcomes as unanimity rule in finite games if proposals are random, sincere, or strategic. We test the two sets of conjectures in a two dimensional framework using laboratory experiments. Our results suggest: 1) majority rule enters the Pareto set more quickly than unanimity rule, 2) majority rule leaves the Pareto set at the same rate as unanimity rule, and 3) majority rule is more likely to select a Pareto optimal outcome than unanimity rule in the final round of play. Our results also suggest that proposers do not behave observationally-rational in the final round and complete information does not affect the primary result. ..PAT.-Unpublished Manuscript [ABSTRACT FROM AUTHOR]