The relative reactivity worth of several B10F3 gaseous coupons has been determined at pressures up to 4.2 atmospheres. These worth values are compared with equivalent B10 loading as B4C dispersed (100 mesh or less) in stainless steel. Gaseous boron is more than five times as effective as the dispersed boron due to particle self-shielding. Bulk self-shielding becomes important only at high concentrations. The gaseous coupons are also compared with two alloy coupons (normal B10 and enriched B10).