The Phelps and Gorham Purchase was the purchase in 1788 of 6,000,000 acres (24,000 km2) of land in what is now western New York State from the Commonwealth of Massachusetts for $1,000,000 (£300,000), to be paid in three annual installments, and the pre-emptive right to the title on the land from the Six Nations of the Iroquois Confederacy for $5000 (£12,500). A syndicate formed by Oliver Phelps and Nathaniel Gorham bought preemptive rights to 6,000,000-acre (24,000 km2) in New York, west of Seneca Lake between Lake Ontario and the Pennsylvania border, from the Commonwealth of Massachusetts.
Phelps and Gorham then negotiated with the Seneca nation and other Iroquois tribes to obtain clear title for the entire parcel. They acquired title only to the lands east of the Genesee River plus the 12 miles (19 km) by 24 miles (39 km) Mill Yard Tract along the river's northwestern bank. Within a year, monetary values rose and, in combination with poor sales, the syndicate was unable to make the second of three payments for the land west of the Genesse River, forcing them to default on exercising the remainder of the purchase agreement. They were also forced to sell at a discount much of the land they had already bought title to but had not yet re-sold; the purchaser was Robert Morris of Philadelphia, financier, U.S. Founding Father, and Senator. In some sources, the Phelps and Gorham Purchase refers only to the 2,250,000 acres (9,100 km2) on which Phelps and Gorham were able to extinguish the Iroquois' aboriginal title.