The purpose of this study was to investigate the effect of injectant stagnation temperature and molecular weight variation on the flowfield generated from secondary injection of a gas normal to a supersonic stream. Experiments were conducted at a primary stream Mach number of 2.80 in the Naval Postgraduate School supersonic wind tunnel. Experimental data have been correlated with various theories, showing both agreement and disagreement. Data presented include penetration of secondary jet into primary flow and shock shape as correlated with the second-order blast wave theory. Jet momentum, not jet mass, was found to be the main determinant of the observed jet effects.