Biodiesel cannot directly be used in diesel engines because some of its fuel properties which poorly affect engine operation but it can be blended with diesel fuel or alcohols. It is important to research fuels with high biodiesel concentration which can be alternatives to diesel and B20. 1-Pentanol, a higher alcohol, shows promise as an alternative fuel used as a fuel additive in diesel and/or biodiesel in compression ignition engines. The purpose of this study is to investigate the effect of the use of 1-pentanol in waste oil methyl ester (B) and diesel fuel (D) on the exhaust emissions and performance of a diesel engine operating at various loads, 0, 3, 6, and 9 kW, with a constant engine speed (1800 rpm). 1-Pentanol (10% and 20% by volume) was added to diesel fuel and waste oil methyl ester to create the following fuel blends: D90P10, D80P20, B90P10, and B80P20. Basic fuel properties were investigated and determined to be within the limit of standards. According to the engine test results, the brake specific fuel consumption (BSFC) and exhaust gas temperatures (EGT) increased with the addition of 1-pentanol to diesel and biodiesel. Testing shows that the brake thermal efficiency (BTE) decreased for the diesel fuel blends D90P10 and D80P20. In contrast, biodiesel blends B90P10 and B80P20 exhibited an increase in BTE. Diesel blends D90P10 and D80P20 increased carbon monoxide (CO) and unburned hydrocarbon (HC) emissions while reducing the production of the oxides of nitrogen (NOx). Compared to other biodiesel blends, B80P20 reduced the production of CO, HC, and NOx emissions at 0 and 3 kW loads while increasing the production of these emissions at 6 and 9 kW loads. (C) 2017 Elsevier Ltd. All rights reserved.