An experimental study was conducted on a diesel engine fueled with ultra-low sulfur diesel (ULSD), palm methyl ester (PME), a blended fuel containing 50% by volume each of the ULSD and PME, and naturally aspirated hydrogen, at an engine speed of 1800 rev min(-1) under five loads. Hydrogen was added to provide 10% and 20% of the total fuel energy. The following results are obtained with hydrogen addition. There is little change in peak in-cylinder pressure and peak heat release rate. The influence on fuel consumption and brake thermal efficiency is engine load and fuel dependent; being negative for the three liquid fuels at low engine loads but positive for ULSD and B50 and negligible for PME at medium-to-high loads. CO and CO2 emissions decrease. HC decreases at medium-to-high loads, but increases at low loads. NOx emission increases for PME only but NO2 increases for the three liquid fuels. Smoke opacity, particle mass and number concentrations are all reduced for the three liquid fuels. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.