Developed acreage is spaced or assignable to productive wells. Undeveloped acreage is acreage on which wells have not been drilled or completed to permit commercial production and that may contain undeveloped proved reserves. The gross undeveloped acres that will expire in 2009, 2010 and 2011 if production is not established by certain required dates are 5,707, 8,290 and 4,720, respectively.