ONIX is an automatic programming system being developed for use by petroleum scientists who may not be knowledgable about computers. As a first step, a system has been implemented to assist in the trial-and-error process of developing new models and techniques for quantitative interpretation of well logs. The user interface exploits graphical techniques to enable petroleum scientists to describe their models in the natural concepts of the domain. The resulting specification can be implemented in any of several different target languages. The system is in active use by petroleum scientists, who find that it has significantly reduced the time to get feedback on hypothesized models.