Law on requirement that it be in writing and signed by both parties.
USINESS AND COMMERCE CODE
TITLE 3. INSOLVENCY, FRAUDULENT TRANSFERS, AND FRAUD
CHAPTER 26. STATUTE OF FRAUDS
Sec. 26.01. PROMISE OR AGREEMENT MUST BE IN WRITING. (a) A promise or agreement described in Subsection (b) of this section is not enforceable unless the promise or agreement, or a memorandum of it, is
(1) in writing; and
(2) signed by the person to be charged with the promise or agreement or by someone lawfully authorized to sign for him.
(b) Subsection (a) of this section applies to:
(1) a promise by an executor or administrator to answer out of his own estate for any debt or damage due from his testator or intestate;
(2) a promise by one person to answer for the debt, default, or miscarriage of another person;
(3) an agreement made on consideration of marriage or on consideration of nonmarital conjugal cohabitation;
(4) a contract for the sale of real estate;
(5) a lease of real estate for a term longer than one year;
(6) an agreement which is not to be performed within one year from the date of making the agreement;
(7) a promise or agreement to pay a commission for the sale or purchase of:
(A) an oil or gas mining lease;
(B) an oil or gas royalty;
(C) minerals; or
(D) a mineral interest; and
(8) an agreement, promise, contract, or warranty of cure relating to medical care or results thereof made by a physician or health care provider as defined in Section 74.001, Civil Practice and Remedies Code. This section shall not apply to pharmacists.