Here,　a　large-scale　char　atomistic　structure　(41,438　carbon　atoms)　and　simple　simulation　approaches　explored　char　gasification　behavior　for　H2O　and　CO2　—　comparing　their　mixture　with　one　gas　being　passive　(non-reactive)　and　the　dual　reactive　mixture.　Reactivity　was　captured　through　simplistic　atomistic　simulations　via　an　automated　sequence　of　gas　diffusion,　close-contact　determination　for　gas　(es)　to　reactive　edge　sites,　then　“reaction”　via　atom　deletion.　The　higher　reactivity　of　H2O　was　captured　by　a　reaction　probability　function.　For　the　reactive　mixture　(where　both　gases　are　reactive),　the　char　consumption　rate　was　14%　higher　than　with　H2O　alone,　but　lower　(∼80%)　than　the　sum　of　the　individual　gases　(where　only　one　gas　is　reactive),　demonstrating　competitive　behavior.　The　H2O　out　competed　the　CO2　molecules　and　contributed　∼83%　to　the　char　consumption　—　with　the　reaction　rate　being　similar　to　that　of　H2O　independently.　The　pore　size　development　for　individual　gases　also　differed　with　H2O　favoring　development　in　the　smaller　pore　sizes　in　comparison　to　CO2.　With　fewer　gas　molecules　(using　10%　to　capture　a　lower　pressure),　the　competitive　behavior　was　muted　and　became　much　closer　to　additive　behavior.　These　simple　simulations　are　consistent　with　the　emerging　rationalization　of　contributing　factors　to　char　gasification.　©　2018　Elsevier　Ltd