The Fluid Catalytic Cracking process, since its discovery in the early 1920s, became an inherent part of petroleum refinery operations. It plays an important role in upgrading feedstock, which typically comprise of high molecular weight hydrocarbons, to lower molecular weight products like Gasoline, Diesel, and LPG. In addition to volumetric expansion, these products enjoy also higher value markup against their initial raw materials. While the chemical composition of the feedstock affects the slate and quality of major FCC products, the FCC catalyst and unit operating conditions unlock the feedstock potential to produce those valuable products thus influencing the whole refinery economics. Understanding complex interactions between the feedstock, the catalyst, and FCC unit operating conditions is the key to proper catalyst selection and optimum unit operation. As the market conditions fluctuate over time so does the economic value of major feed cracking products that may require adjustment to the catalytic system and/or operating conditions to achieve a new operational and financial optimum. The same concept applies when the FCC feedstock’s properties change since they are blends of virgin and preprocessed crude oils and refinery streams of low economic value. To understand and study those intricate relations, over a hundred FCC feeds, originating from diverse geographical locations around the world, covering a wide range of properties, and including ones that require special initial preprocessing, were assembled. Extra effort was made to assure that this collection represents the type of feeds that are used by the industry today, including North American shale oil. All feeds were thoroughly characterized for physical and chemical properties using standard industry methods [1], and they were evaluated in the ACE apparatus against three families of commercial FCC catalysts using a range of severities (cat-to-oil ratio from 0 to 100, and reactor temperatures from 778 to 817 K). These catalysts were laboratory-deactivated using the Cyclic Propylene Steaming, a metal-free deactivation protocol. The rationale for using metal-free deactivation, besides simplifying the analyses, was to focus on the catalyst-feed interactions during the cracking process. Cracking products were identified and thoroughly characterized. All these experimental data were used to develop a model that allows for predicting major cracking product yields in the ACE unit while taking into account feed properties and operating conditions. Based on a snapshot of market prices of major cracking products, different market scenarios were simulated and optimum operating conditions to maximize operation economics were discussed. This paper examines also the effect of adding low cost and low quality opportunistic feeds to the FCC unit feed blend on operations economics. At the end it provides helpful guidelines for FCC engineers on the effect of feed properties on the FCC unit operations, process optimization, and profit maximization.