Montana Title 28. Contracts and Other Obligations § 28-11-105. When guaranty considered original obligation and need not be in writing

(1) when the promise is made by one who has received property of another upon an undertaking to apply the property pursuant to the promise or by one who has received a discharge from an obligation, in whole or in part, in consideration of the promise;

(2) when the creditor parts with value or enters into an obligation in consideration of the obligation in respect to which the promise is made, in terms or under circumstances that render the party making the promise the principal debtor and the person in whose behalf the promise is made the party's surety;

(3) when the promise, being for an antecedent obligation of another, is made upon a consideration:

(4) when a factor undertakes to sell merchandise for a commission and guarantee the sale;

(5) when the holder of an instrument for the payment of money upon which a third person is or may become liable to the holder transfers the instrument in payment of a precedent debt of the holder's own or for a new consideration and in connection with the transfer enters into a promise respecting the instrument.