Diesel engines are one of the most common reciprocating engines for use in many applications that convert the chemical energy in the fuel into kinetic energy. Veg-etable oils are viewed as an alternative fuel or sustainable fuel and are utilized straightforwardly in diesel engines. Since these oils are sustainable and ecological amicable. The injection pressure of diesel engines can be altered to help ensure that the viscosity of the vegetable oils is low enough to allow proper atomization of the fuel. Waste vegetable oils can also be blended with diesel fuel for use under a wide range of conditions. The injection pressure is one of the important variables affecting the emissions of the engine. In this experimental study: the effect of changing the injection pressure 170, 185 and 200 bars on the emissions of a diesel engine by using different types of blends of waste vegetable oils with diesel fuel was studied. The important results are that with an increase in injection pressure it leads to reduce carbon monoxide in a range of percentages from 5% to 35%, as well as reducing carbon dioxide emissions in a range of percentages from 2% to 12% compared to the 170 bar injection pressure at different loads. Carbon dioxide is one of the main pollutants that cause an increase in global warming, and the use of these oils with a change in injection pressure has led to a further decrease in carbon dioxide emissions, and thus a decrease in global warming.