Diverse additives were subjected to a series of three screening phases to assess their suitability with a steam drive process for recovery of tar sand and heavy oil resources. The resources studied were tar and mateials from Utah and Alberta and heavy oil materials from California and Saskatchewan. The first screening phase, which consisted of a literature review, identified over 120 potential additives to steam processes. In the succeeding screening phases, these additives were subjected to semiquantitative laboratory evaluations using actual resource materials. Chemical and physical evaluations were conducted during the second screening phase to assess additive enhancement of steam process oil recovery mechanisms, additive thermal stability at steam process temperatures, and additive/matix interactions. Additives demonstrating potential enhancement of steam process oil recovery, adequate thermal stability and acceptable additive/matrix interactions were subjected to process simulations in unscaled physical models during the third and final screening phase. The hot water region of the steam drive process was simulated with a hot water drive in an elemental core apparatus. Improvements in oil recovery were established by comparing oil recovery from simulations with additives to a baseline run without an additive. A total of 46 Phase 3 tests were performed. A list of additive/resource combinations which demonstrated increased oil recovery was compiled. 5 refs., 18 figs., 35 tabs.