Developing engine oil formulations for today's marketplace requires a careful balance between cost and performance. Definition of optimized formulations requires detailed knowledge of the quantitative relationships between performance, or deposit control, and additive component concentrations. To develop these relationships, a series of multigrade engine oils formulated with two levels of a dispersant olefin copolymer VI improver were evaluated using the Caterpillar 1H2 engine test procedure. The performance package components and/or their levels in these oils were varied according to statistically designed, fractional factorial patterns. This approach provides an estimate of the effect of each component and their interactions. It also provides insight into the inherent test variability associated with TGF, WTD and the land and groove deposits which make up these ratings.