Parametirc dependence of laser-induced breakdown spectroscopy (LIBS) for detection of trace elements has been studied. LIBS was applied for quantitative measurements of environmentally important trace metals such as magnesium, lead, copper, and calcium in oil samples. This work incorporates investigations of LIBS experimental paraments such as the distance between the plasma and optical fiber, sample rotation speed, laser pulse energy, gate delay, and position of the focal spot on the pellets. The optimized parameters are tested for the preparation of the calibration curves for Mg, Pb, Cu, and Ca. Limits of detection (LOD) of our LIBS system were also estimated for these elements. The system was applied for trace metals detection in Arabian crude oil residue samples which is not trivial to detect with conventional techniques.