The Bureau of Mines performed laboratory research into the effects of a barium-based fuel additive (the "postflame" type) on diesel particulate matter (dpm) emissions. The 5.6-L, six-cylinder test engine is typical of types certifiable for use in underground mines. Test parameters consisted of additive concentration and engine loads, speed, and air intake restriction. Dpm emissions, including condensed volatiles, were measured gravimetrically. Also measured were gaseous emissions including carbon monoxide, nitrogen oxides, and hydrocarbons. The fuel additive was effective, reducing dpm up to 75 pct, when used at a concentration of 0.09 Wt pct (one-fourth of the concentration recommended by the manufacturer). The additive was most effective at the highest fuel-air ratios, reducing dpm from 400 mg/m3 for untreated fuel to 120 mg/m3. At light loads, 25 pct of full rated, no dpm reductions were measured. Based on these results, the additive is recommended for use in diesel fuel, at a concentration of 0.09 Wt pct, to power underground mining equipment as long as certain conditions are met: that a beneficial dpm reduction is verified, that the minimum required quantity of additive is used, and that potential adverse effects such as increased nitrogen oxides are checked.