it depends. different program has different requirement.
mba requires gmat. most phd pregram prefers gmat.
but some programs in some schools may require gre.
for example, wharton seems to prefer gre, or what we can say,
those programs prefer gre.
http://www.wharton.upenn.edu/doctoral/admissions/scores.html
>>Either the Graduate Management Admissions Test (GMAT) or the Graduate Record >>Examination (GRE) may be taken for admission to most programs. For Business >>and Public Policy, Operations and Information Management, Real Estate, and >>Statistics, only the GRE is acceptable.
so u should check one by one
