How would you prove the existence and terms of an oral agreement if
there were no third parties present to overhear the agreement?

Hi! Thanks for the interesting question.

In the legal circles, it is widely known that like written contracts,
their oral counterparts are indeed admissible in court. But the
reality is that it is quite difficult to prove them.

“The classic definition of a contract requires an offer, acceptance of
that offer, and some proof that there was intention to create a
binding agreement. All of these can be proven by verbal evidence of
words spoken, or actions, which show the necessary intention. The
source of the misleading saying lies in the difficulty that sometimes
exists in proving what the agreement was. If that can’t be proven,
courts will not ‘make an agreement’ for the parties. So many oral
understandings turn out to be misunderstandings, and unenforceable.
Assuming that any particular bargain is unenforceable, however, is a
bad idea. If the other side sues, you face huge legal costs, and the
prospect of paying damages, interest, and the other party’s lawyer.
For this reason, it is always best to ‘put it in writing’.”

“Is An “Oral Contract” Worth The Paper Its Written On?”
http://www.weilers.ca/QuickTips/index.asp?ID=63 

An online legal dictionary meanwhile provides a general idea on how
oral contracts can be proven.

“An oral contract is often provable by action taken by one or both
parties which is obviously in reliance on the existence of a
contract.”

“Oral Contract”
http://dictionary.law.com/definition2.asp?selected=1407&bold=%7C%7C%7C%7C

Such a pronouncement above can be rather vague so an example is in
order. Our last link, although it came from a website from India,
cites an American article which uses the entertainment industry as an
example on how an oral agreement can be proven.

“I always recommend that my clients secure a written agreement
whenever possible. If the situation does not lend itself to a written
agreement, then create a paper trail i.e., after a pitch meeting send
the executive a letter thanking them for their time and reiterating
the purpose of the meeting; when you are hired, or are hiring someone,
send a letter accepting or confirming the acceptance of the position.”

In an example like this, it is easy to see that such tips can be
adapted to different contracts as well and not only to the
entertainment industry.

“Legal Ease ‘The Power of the Spoken Word’”
http://www.legalserviceindia.com/articles/article+d.htm 

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Easterangel-ga           
Google Answers Researcher

Satisfactory answer. Thanks