Sale Contingent Upon Other Purchase

[JP S.]

Hi,

I would like to tie up a potential seller's property A for an assignment. He tells me the sale of his property is contingent upon his purchase of another property B. (He apparently has an offer in on an REO or maybe a short sale.)

Can I tie up property A right now with a contract that has such a contingency written in? Will this fly, especially considering I'm going to sell the contract? Or should I wait until the seller has made the succesful purchase of property B before making my offer.

Thanks,
jp