Okla. Stat. tit. 15, § 219A

A. A person who makes an agreement with an employer, whether in writing or verbally, not to compete with the employer after the employment relationship has been terminated, shall be permitted to engage in the same business as that conducted by the former employer or in a similar business as that conducted by the former employer as long as the former employee does not directly solicit the sale of goods, services or a combination of goods and services from the established customers of the former employer. B. Any provision in a contract between an employer and an employee in conflict with the provisions of this section shall be void and unenforceable.