Dot gain has been recognized as one of the most significant factors affecting offset printing quality. Since it is not possible to entirely eliminate dot gain, better control of this problem is one of the goals of this study. The main purposes of this study were (1) to identify the most important factors that influence the percentage of "on press" dot gain using the sheet-fed offset lithography press, and (2) to establish optimum process operating conditions so that the minimum yield of dot gain size utilizing the Heidelberg GTO could be obtained;A randomized 24 factorial experiment was conducted in which every factor was run at two specified levels (fixed effects) determined by the practical operating conditions on the Heidelberg GTO sheet-fed offset press at a large major midwestern university. The four factors were (1) fountain solution pH, (2) paper types (coated vs. uncoated), (3) plate-to-blanket pressure, and (4) blanket-to-paper pressure;Overall the results suggested that the main effect of paper was the dominant variable affecting on press dot gain. A stepwise regression analysis revealed that the main effect of paper was so overwhelming that it outweighed the significance of the other effects. Thus, the paper factor was controlled for a second statistical analysis to study the conclusive relationships among the other variables and obtain more accurate estimations for their associated effects. The findings of the second analysis yielded the following recommendations: (1) For prints that require high fidelity and emphasize highlight areas, the process should use coated paper with a combination of lower blanket-to-paper pressures, higher plate-to-blanket pressures, and higher fountain solution pH values. (2) For prints that require high fidelity and emphasize midtones and shadows, the process should use coated paper with a combination of lower blanket-to-paper pressures, lower plate-to-blanket pressures, and lower fountain solution pH values. (3) The optimum process using the uncoated stock for the Heidelberg GTO was not recommended simply because the process was not stable and capable.