PHD IN USA AFTER DOIING MBA IN MARKETING

Hello all, I have done my Engg in cs and Mba in marketing.i now want to do PHD from USA in some business management subject. Which exam i have to appear for …gre or gmat? and is there any necessity of work experience? kindly reply…very u…

Hello all,
I have done my Engg in cs and Mba in marketing.i now want to do PHD from USA in some business management subject.
Which exam i have to appear for ..gre or gmat?
and is there any necessity of work experience?
kindly reply..very urgent.
thanks a lot