Since Tubelite and Risica did not agree to a specific interest rate, the statutory rate of six percent is by law read into the agreement. It is the maximum rate of interest allowed on this type of transaction. Houston Sash Door Co. v. Heaner, 577 S.W.2d 217, 221 (Tex. 1979); Amarillo Equity Investors, Inc. v. Craycroft Lacy Partners, 654 S.W.2d 28, 30 (Tex.App. — Fort Worth 1983, no writ); Tex.Rev.Civ.Stat.Ann. art. 5069-1.03 (Vernon 1987).
Id. In Amarillo Equity Investors v. Craycroft Lacy Partners, 654 S.W.2d 28 (Tex.App. — Ft. Worth 1983), another appellate court adopted the same interpretation of the issue. Id. at 30-31.
A charge of 18% interest, moreover, is more than twice the 6 percent allowed by law and subjects the party to the harsher penalties of subdivision 2. See Amarillo Equity Investors, Inc. v. Craycroft Lacy Partners, 654 S.W.2d 28, 30 (Tex.App. — Fort Worth 1983, no writ); Flato Electric Supply Co. v. Grant, 620 S.W.2d 915, 917 (Tex.Civ.App. — Corpus Christi 1981, writ ref'd n.r.e.). In order for Fish Oil's demand for interest in the present case not to be usurious, the work tickets must constitute valid written agreements to pay interest at 18%.