Weekly passive sampling campaigns were carried out over two sample periods to measure volatile organic compounds (VOCs) in Bursa, one of the most heavily industrialized cities in Turkey. The measurements, taken at 40 points in October 2005 and 49 points in April 2006, revealed concentrations of 34 VOCs, including aromatics, olefins, paraffin and halogenated compounds; with benzene, toluene, ethylbenzene, and o, m, and p-xylene polymers (BTEX) being the most abundant compounds detected at all sample points. Toluene was the most abundant VOC found at all sites, with a median concentration ranging from 0.99 mu g/m(-3) in background samples to 35.98 mu g/m(-3) at industrial sites, followed by m-and p-xylene and ethylbenzene. High toluene-to-benzene (T/B) ratios (9.6) were observed at industrial sites, whereas the T/B ratios measured in urban areas and at roadside locations were comparable and were higher than in other countries. A principle component analysis (PCA) using a receptor-oriented source apportionment model was applied to the VOC data and extracted four major sources for both the October and April sampling periods. Principle factors accounted for 85% and 74% of the variance in VOC data for the October and April sample periods, respectively. The identified sources of VOCs in Bursa included: 1) vehicular exhaust (gasoline and diesel engine vehicles), 2) industrial emissions, and 3) evaporative emissions. The explained factors indicated that the urban air in Bursa was influenced by both traffic and industrial sources, each of which displayed different levels.