Hydrogen and carbon monoxide generated on board of vehicles from liquid fuels have great utility for solid oxide fuel cells or as reductant for lean NOx emission control systems. In order to make onboard fuel processing a reality, durable fuel reforming catalysts must be developed because current reforming catalysts are incapable of processing commercial fuels without deactivation. Carbon deposition represents a significant technological challenge to the development of a viable fuel reforming catalyst. In order to reduce reforming cost and increase the lifetime of catalysts and the yields of reforming products (hydrogen and CO), there are optimal relationships among steam to carbon ratio, oxygen to carbon ratio, and reforming temperatures depending on the types of fuels and catalyst formulations. In this work, we are going to address the effects of O/C ratio and calcination temperature on dodecane ATR over Ni-monolith catalysts. The yields of reforming and cracking (C1-C4 hydrocarbons) products were compared with changing O/C and catalyst calcination temperatures. Based on characterization of fresh and used catalyst post ATR, the role and deactivation of the Ni component are investigated. The relative contributions of homogeneous cracking reactions versus catalytic reforming reactions are discussed.