Twelve Holstein steers (454 ± 32 kg) with cannulas in rumen and proximal duodenum were used in a generalized randomized block design to compare steam-flaked corn (SFC), barley (SFB), wheat (SFW), and oats (SFO) as grain sources (74% of diet dry matter, flake density = 0.31 kg L^-1) on characteristics of digestion. Ruminal organic matter (OM) digestion was similar for SFC-, SFB-, and SFW-based diets, but lower for SFO. Ruminal microbial efficiency was greater for SFW and SFO. Given that the undegradable intake protein (UIP) value of SFC is 57%, the comparative UIP values for SFB, SFW, and SFO were 39.8%, 36.1%, and 47.3%, respectively. Ruminal starch digestion was lower for SFC than the other flaked grains. Total-tract OM digestion and digestible energy were greatest for SFC, intermediate for SFB and SFW, and lowest for SFO. Given the net energy maintenance (NE_m) value of SFC is 2.40 Mcal kg^-1, the comparative NE_m value for SFB, SFW, and SFO were 2.25, 2.36, and 2.17 Mcal kg^-1, respectively. Steam flaking results in important modifications of small grains that appreciably affect their comparative feeding value. Current standards underestimates the NE value of SFB, SFW, and SFO, and overestimates the UIP values for SFB and SFO.