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The determination of Mn, Fe, Co, and Zn was performed in gasoline, jet, and diesel fuel samples by electrothermal atomic absorption spectrometry using the Transverse Heated Filter Atomizer (THFA). Thermal conditions were experimentally defined for the investigated elements. The elements were analyzed without the addition of chemical modifiers, using organometallic standards for the calibration. Gasoline samples were analyzed directly, while jet and diesel fuel samples were diluted 1+3 with n-heptane. The following LODs were obtained using 40 µL injections: 0.08 µg/L Mn, 0.35 µg/L Fe, 0.54 µg/L Co, and 0.06 µg/L Zn. The limits of determination, calculated for diesel and jet fuel samples, were 1.2 µg/kg Mn, 4.9 µg/kg Fe, 7.6 µg/kg Co, and 0.8 µg/kg Zn. The corresponding limits of quantitation for gasoline samples were about four times higher. KEYWORDS: electrothermal atomic absorption, transverse heated filter atomizer, gasoline, diesel fuel, trace elements Introduction Electrothermal atomic absorption represents a suitable instrumental technique for the analysis of elements in petroleum products [1–5]. The technique shows very low detection limits, similar to or even better than those found for other spectroscopic techniques, such as Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) [6] and ICP-Mass Spectrometry (ICP-MS) [7–12]. Some problems were evidenced in the use of ETAAS when elements like Ni [3] and Pb [13] are analyzed, due to the different behavior of organo-metallic species during the thermal treatment of standards and samples. Recently, the use of transverse heated filter furnace for the analysis of trace elements in automotive fuels was proposed [14]. This instrumental technique showed interesting results for volatile elements, such as Cd and Pb. The filter furnace approach was the subject of several papers and of continuous developments in order to improve the design [15], to extend the range to low volatile elements [16], to employ the furnace in transverse heated atomizers [17], and to determine trace elements in aqueous and organic solutions [18,19]. The most interesting aspects of the filter furnace concept are: the capability to inject large volumes due to the large volume of the zone allocated to the sampling, the limited non-specific absorption by molecular species due to the filtering action of the furnace, and no need for chemical modifiers due to the furnace design.