Seong Cheol Park Texas A&M AgriLife Research   PO Box 1658 1708 US Highway 70S Vernon, TX 76385 U.S.A.   scpark@ag.tamu.edu   http://agecon.tamu.edu/faculty-staff/faculty/park-seong/           JEL Areas: Q0 : Agricultural and Natural Resource Economics; Environmental and Ecological Economics: General Q3 : Nonrenewable Resources and Conservation: General