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Base metal oxide diesel oxidation catalyst technology having low sulfate making tendencies was evaluated using the ECE R-49 Test procedure on medium and heavy duty diesel engines and found to achieve substantial reduction of particulate, gas phase HC and CO emissions. Although the engines met the current European standards, further reduction in these emissions for vehicles operated in congested urban areas, such as buses, would have a positive impact on general air quality. A study of varying fuel sulfur levels (110-770 ppm S) showed that the catalyst was effective for control of sulfate-make such that overall particulate removal in the test was not compromised. However, it was found that lower fuel sulfur levels (< 550 ppm S) gave the best results for the ECE R-49 test which places emphasis on test modes yielding the highest exhaust temperatures.