Believe it or not, the old-fashioned "handshake" began as a means for two people to assure one another that neither was carrying a weapon. Over the years, this simple gesture has evolved into a contractual symbol—or a guarantee—for an oral agreement. But in an era of phone-book sized contracts, fine print and legal battles, does time-honored handshake deal still carry any weight?

The answer is yes—as long as you can prove it in court.

If an e-mail or chain of e-mails clearly states an offer for entering into a deal with all of the material terms and the other side responds by e-mail accepting the terms, then there's a good chance that a valid contract has been formed — even though no signatures have been exchanged. So be careful. If all you intend is to negotiate the issues leading to a formal written and signed contract accepted by both parties, make sure you say that in your e-mails.

Generally, oral or verbal contracts are indeed legally enforceable, but there's a fundamental problem: how do you prove what was agreed upon? That's why written contracts are far more useful, because everything's down in, well, black and white.
Read more at http://www.askdavetaylor.com/are_verbal_contracts_legally_enforceable.html#giafXjivC7k2GBuK.99