In Laramie Rivers Co. v. Pioneer Canal Co., 565 P.2d 1241, 1245 (Wyo. 1977), the Court clarified that a mere difference of opinion as to the amount due or as to liability does not preclude prejudgment interest if the amount sought to be recovered is a sum certain and the party from whom payment is sought receives notice of the amount sought. In Laramie Rivers, the amount sought to be recovered was established prior to entry of judgment by a written billing statement for a fixed amount. The Court remanded the case to district court for determination of when the debtor received notice of the fixed amount claimed.