Transactions may be made orally or in written (simple or notarial) form.

A transaction for which a statute or agreement of the parties has not established a written (simple or notarial) form, may be made orally.

Unless otherwise established by agreement of the parties, all transactions that are performed upon their concluding may be made orally, with the exception of transactions for which notarial form is established and transactions for which nonobservance of simple written form entails their invalidity.

Transactions in performance of a contract concluded in written form, may by agreement of the parties be made orally, if this does not contradict a statute, other legal acts, or the contract.

A transaction that may be made orally shall be considered concluded in the case when from the conduct of a person his will to conclude the transaction is apparent.

Source: Iravaban.net