We report on the use of formal methods and supporting tools during the development of a language applied in a banking environment. This language, called RISLA, is used to define the nature of the interest products offered by a bank. A RISLA description fixes the cash flows (amounts of money coming in or going out on particular dates) resulting from a product, and is used to generate COBOL code. The language has been developed with the use of algebraic specifications, the role of which is discussed. Note: An extended abstract appeared under the same title in M. Wirsing (editor), Proceedings of the ICSE-17 Workshop on Formal Methods Application in Software Engineering Practice, Seattle, April 1995. Keywords & Phrases: algebraic specifications, financial engineering, COBOL, formal methods experience, tool support; Work done while at CWI, P.O. Box 94079, 1090 GB Amsterdam, The Netherlands. y Work done while at the Programming Research Group of the University of Amsterdam. 1 Intro...