Appellee Perkins sued appellant, National Life Insurance Company, for the recovery of commissions alleged to be due him in connection with the sale of 476 acres of land to Gifford-PIill & Company. Upon the conclusion of the testimony appellant presented its motion for a peremptory instruction, which was overruled. Thereupon the court submitted certain special issues to the jury, in response to which the jury found that the parties had entered into a contract by the terms of which appellee would receive a commission on the value of the gravel, sand and ballast content of the land in question in event the services performed by him “were the procuring cause of the sale of the total real estate to a purchaser”; that the services performed by appellee in connection with the sale of the land to Gif-ford-Hill & Company were the procuring cause of the sale; and that $1,884.96 was the sum of money, if then paid in cash, to which appellee was entitled for his services in connection with the sale. Ap-pellee moved for judgment on the verdict and appellant moved for judgment non obstante veredicto. The court overruled the motion of appellant, granted the motion of appellee, and rendered judgment for the sum found by the jury, and hence this appeal.
Appellant says the trial court erred in overruling its motion for a directed verdict and its motion for judgment non ob-stante veredicto, because: (1) the only contract proved by appellee was one by which appellant agreed to pay him for his aid in selling a sand and gravel lease, for which he received full payment; (2) appellee adduced no competent evidence of probative force 'to show that he was employed by appellant to aid in the sale of the land or its sand and gravel content; and (3) appellee adduced no evidence to show that he rendered any service in effecting the sale of the land to Gifford-Hill & Company or as to what would be reasonable compensation for such service. It therefore contends that the judgment of the trial court should be reversed and that judgment should be here rendered in its favor. On the other hand, appellee contends that the evidence was sufficient to sustain the verdict and consequently the judgment appealed from should be affirmed.
In passing upon the foregoing contentions it is the duty of this court to view the record before us in its most favorable light from the standpoint of appellee. Besteiro v. Besteiro, Tex.Com.App., 65 S.W.2d 759. When thus viewed, if there was no evidence of probative force raising one or more of the ultimate fact issues found by the jury, then the .judgment appealed from should be reversed; but if there was competent evidence of probative force raising such issues, then the judgment should be affirmed. Wichita Falls & O. R. Co. v. Pepper, 134 Tex. 360, 135 S.W.2d 79.
Neil Thomason testified that he was manager of appellant’s investment department and as such had charge of the disposition of its real estate subject to the approval of the home office; that the land here involved was known as the Camp farm and was acquired by appellant in 1933; it was his duty to find a buyer or lessee for the farm and before contacting appellee he had tried unsuccessfully to sell or lease the same to Gifford-Hill & Company, who was engaged in the gravel business ; he had known appellee for about ten years, during a part of which time appel-lee was engaged in operating a gravel pit near the Camp farm; extensive tests made on appellant’s farm for grayel prior to 1935 did not “show up very favorably” or indicate the presence of gravel in commercial quantities; in the early part of 1935 he had a conversation with appellee with respect to the possibility of getting gravel operations started on the Camp farm; and that he thought appellee could help him make a sale or lease of the property to someone.
Appellee testified, in substance, that Thomason approached him in the early part of 1935 concerning gravel operations *541on the Camp farm, and at that time he agreed to “work out a proposition with him to handle his gravel operations and dispose of it on some percentage basis”; he and Thomason later agreed upon a basis of fifteen per cent commission; he explained to Thomason fully and in detail at the time of their agreement how he expected to proceed in his efforts to consummate the proposed transaction; after the verbal agreement had been entered into he took a crew of men out on the Camp farm and made extensive tests by which he discovered and later demonstrated to an engineer for Gifford-Hill & Company the presence of gravel in commercial quantities on about 45 acres of the farm; thereafter, when it became apparent that a favorable lease contract would be entered into between appellant and Gifford-Hill & Company, Thomason requested him to reduce the amount of his commissions to ten per cent, which he agreed to do; he made |:hree or four trips to Dallas prior tc May 27, 1935, for the purpose of conferring with Thomason in regard to the project; and that the ten per cent commission was to apply to “any money that was derived from the sale of sand and gravel from that Camp farm.” In response to a specific question from his counsel as to whether his conversations and negotiations with Thomason related only to a lease contract, or to a disposition of the sand and gravel under the Camp farm, appellee testified: “I would receive a commission on all the sales relative to sand and gravel, or the sale of sand and gravel on the farm in any manner.”
On May 27, 1935, appellant entered into a written lease contract with Gifford-Hill & Company, by the terms of which it leased the Camp farm for ten years, and so long thereafter as marketable sand and gravel might be available in paying quantities not to exceed twenty years, in consideration of certain royalties to be paid on the sand and gravel removed therefrom; provided, however, that if the lessee should not begin operations within a period of ninety days from the effective date of said lease, it should pay to appellant $200 per month as guaranteed advanced royalty until operations were started. Lessee paid to appellant the sum of $200 per month until on or about September 8, 1938, at which time the lease contract was merged into and terminated by a comprehensive written contract of sale between the parties. Thereafter, on December 12, 1938, appellant conveyed the Camp farm, less a reserved one-fourth interest in the gravel and sand, to Gifford-Hill & Company for a consideration of $35,000 in accordance with the contract of sale. The consideration included a credit of $2,000 for advanced royalty payments previously made under the prior lease. The contract of sale and deed of conveyance each' provided for further credits on prior advanced royalty payments, dependent upon the amount of future royalty payments to be made by grantee under a schedule of royalties covering the interest reserved by grantor in and to all gravel to be mined and removed from said land. Appellant paid to appellee as earned commissions under the lease contract the sum of $20 per month during the continuance of the lease but refused to pay any further commissions on the consideration for the sale and conveyance. There was evidence tending to show the value of the Camp farm for agricultural purposes and its additional value attributable to sand and gravel deposits which was sufficient to warrant the jury in concluding therefrom that the reasonable value of the sand and gravel content of the land conveyed was in excess of the sum of $18,849.60.
In our opinion the evidence to which we have referred, if admissible and competent, was sufficient to raise and sustain the findings of the jury. Appellant insists, however, that all parol testimony as to the terms of the contract sued upon was inadmissible, incompetent and wanting in probative force because the prior verbal negotiations and agreements between the parties were merged into a written contract consisting of certain letters, and the necessary effect of considering such parol testimony was to vary and add to the terms of the written contract, contrary to law.
It is generally, held that where the parties have reduced to writing that which upon its face appears to be a complete and certain agreement, the courts will conclusively presume, in the absence of fraud, accident or mistake, that the writing contains the entire agreement, and under such circumstances parol evidence of prior negotiations, conversations or statements will not be accepted for the purpose of adding to or varying the written instrument. Lewis v. East Texas Finance Co., 136 Tex. 149, 146 S.W.2d 977. On the other hand, where the writ*542ing is incomplete, uncertain or ambiguous, parol evidence is admissible and competent to explain the same or to ascertain the true intention of the parties in so far as such intention is consistent with the writing. Higginbotham Cattle Co. v. Whaley & Lewis, Tex.Com.App., 41 S.W.2d 34. Moreover, “even though a written contract be unambiguous on its face, parol evidence is admissible for the purpose of applying the contract to the subject with which it deals; and if by reason of some collateral matter an ambiguity then appears, proof of the facts and circumstances under which the agreement was made is admissible, in order that the language used in the contract may be read in the light thereof for the purpose of ascertaining the true intention of the parties as expressed in the agreement.” Murphy v. Dilworth, 137 Tex. 32, 151 S.W.2d 1004, 1005.
Appellant relies upon certain letters which it says constituted the written contract between the parties. On May 6, 1935, appellee wrote Thorhason as follows: “In case the gravel deal with either Gifford-Hill or S. & G. Company goes through I agree to accept 10% commission for any help I am able to give in connection with making the deal or in handling the property after the lease is let. The Commission to be paid as the funds are received by the National Life Insurance Company from the lease contract.” On October 11, 1935, Thomason wrote appellee as follows: “Replying to your recent inquiry, wish to advise that our understanding with reference to your commission in connection with the recent gravel contract we have let on the Camp farm reads as follows: ‘We are to pay you 10% commission. The commission to be paid as the funds are received by the National Life Insurance Company from the gravel contract. You are also to render any help we call on you for in connection with the making of the deal or handling, the property after the lease is let.’ ” We do not think it is necessary to set forth other written communications passing between the parties. Appel-lee testified that after his verbal agreements, that is, the agreement for a commission of fifteen per cent and his subsequent agreement to reduce his commissions to ten per cent by reason of the favorable lease contract which was about to be entered into with Gifford-Hill & Company, he wrote Thomason the letter of May 5, 1935, because: “I knew that a lease of at least ten years and the amount of money that I was to receive, that possibly either he or myself might die, or get transferred or something — lie might be transferred and there might be some misunderstanding as to what I was to receive, and I asked that he verify our agreement by letter and he said he would be glad to do it. I waited sometime before it .was verified, and I think I called him or wired him or something, and then he did give me a letter to verify the fact that I was to receive ten per cent.”
We cannot say as a matter of law that the language employed in the letters before us was such as to require the courts to presume conclusively that the same embraced and expressed the entire agreement between the parties. Appellee’s verbal testimony as to the terms of the contract sued upon and his explanation as to why the letters were written is not necessarily inconsistent with the language actually used in such letters. Under the evidence as a whole we think reasonable minds .might differ as to what was meant by the expression “gravel deal”, or “help in making the deal”, or “handling the property after the lease is let”, as contained in the letters. But if such expressions and the amount of the commissions to be paid for the intended services related conclusively and . solely to the lease contract with Gifford-Hill & Company, then what was the • intention of the parties in the event such lease be merged into a contract . of sale, and why was the lease so merged? By reason of the latent ambiguity which arises in thus applying the letters to the subject matter with which they purport to deal, we are of the opinion that parol evidence was admissible to aid in making the application. First Nat. Bank v. Rush, Tex.Com.App., 210 S.W. 531; Blake v. Pure Oil Co., 128 Tex. 536, 100 S.W.2d 1009; Jasper State Bank v. Goodrich, error dismissed Tex.Civ.App., 107 S.W.2d 600. Without further discussion we hold that the competent evidence of probative force in this case was 'sufficient to raise and sustain the ultimate fact issues found by the jury. Texas Creosoting Co. v. Sims, error dismissed Tex.Civ, App., 113 S.W.2d 227.
Finding no reversible error under any of the points' or assignments presented by appellant, the judgment of. the trial court is affirmed.