The 1980's will see the profitable integration of low cost digital computers, powerful process control software, and advanced control and optimization technology in petroleum refineries to reduce plant energy consumption and maximize valuable product yields. This paper surveys the experience of the last two decades for the third and most critical segment: on-line closed-loop optimization technology. The requirements for successful application emphasize practical guidelines, economic scope and justification, model requirements, mathematical algorithms, objective functions, project costs, and maintenance requirements. Matching appropriate models and algorithms to particular process units and business objectives will be outlined. The proper role of steady-state and dynamic optimization will be explained for petroleum refineries.The ingredients to expand technical successes to lasting economic successes are listed. The successful systems have a fundamental impact on the gap between control room operations, higher level management objectives, planning, and environmental restrictions. Beyond the mathematical techniques for solving the problem, much attention is focusing on the information interface between the optimizing computer, the operators charged with running the process, and engineering managers charged with setting operating objectives in response to business and market changes. People need to know much more than what the optimum computer answer is, to be assured the computer optimum is true and to utilize the tool for business control.The systems methodology for successful implementation on crude units, vacuum units, fluid catalytic crackers, catalytic reformers, gas plants, olefins plants, aromatics plants, hydrocrackers, and utilities will be developed. Some optimizations worth $100/day, and some worth $10, 000/day will be described. Future trends for integrated units and refinery wide optimization are given.These examples will clearly illustrate the role on-line process optimization is playing to reduce gasoline shortages and conserve energy.