Energy plays an important role in the economic growth and development around the world. Though conventional oil resources like petroleum and natural gas are still the main sources of energy, the depletion of oil reserves and the continuing soaring oil price indicate that countries should turn to unconventional oil resources as reliable and secure energy sources. Oil shale represents one of the largest hydrocarbon resources in the world [1] . Its utilization has received much attention all over the world due to the rise of oil-prices [2] . The petroleum supply/ cost factors create a need for alternative transportation fuels. Shale oil derived fuels are one of these alternatives, and perhaps should be viewed as the most attractive for several reasons: first, shale oil is a superior source of feedstock for transportation fuels-our single largest domestic energy requirement. Utilizing the gas oil conversion flexibility found in most modern refineries, essentially all of the syncrude can be converted to transportation fuels. Jet fuels, diesel and gasoline can all be produced from syncrude, and by choosing the processing conditions, any product can be maximized. Second, the environmental challenges posed by oil shale development are manageable [3] . Also, oil shale have some potential for the production of several synthetic products such as cement, calcium, alumina, pitches, the carbon adsorbents, zeolites, carbon fibres and other chemicals. These various industrial applications of oil shale have generated in recent years many studies on methods for extracting these oils, such as pyrolysis by conventional heating or under microwave irradiation, extraction with various solvents under sub and supercritical conditions and combustion in fluidized bed reactors [4] . The percentage of organic carbon present can vary from approximately 8 wt% to 81 wt%. The organic material is normally classified into two components: 1) kerogen, a high-molecular-weight material which is insoluble in normal petroleum solvents; and 2) natural bitumen, a lower-molecular-weight substance which is soluble in benzene and other common petroleum solvents. One distinction between oil shale and coal and tar sands is the amount of ash present. Oil shale normally has an ash yield of 33 wt% or more, whereas coal and tar sands have significantly smaller amounts [5] . Carbonaceous shales have a wide distribution on the Egyptian surface and in subsurface sedimentary sequences e.g. in sediments of predominantly Carboniferous, Jurassic, Cretaceous, Paleocene and Eocene age. The carbonaceous and black shales in Egypt gained interest since five decades when the phosphorite deposits were discovered and exploited. The phosphorites are intercalated with and capped by black shales that contain considerable amounts of organic matter and are enriched in trace elements, which may be of economic potential. The interest in the black shales all over the world in the last decades principally stem from the widespread recognition that black shales are important source rocks for petroleum or may be used as natural fuel resources. Various previous studies of the carbonaceous shales in Egypt concentrated on an individual location or an individual geological age. Various techniques for the recovery of shale oil are available such as solvent extraction, thermal decomposition (retorting) [6] -[10] and supercritical fluid extraction [4] [11] . Solvent extraction of organic matter is one of the well-known techniques for dissolving organic matter within rock composite. The soluble kerogen decomposition products are removed from the oil shale matrix into a solvent carrier usually present in excess [12] . Some of the advantages of this process are the process selectivity, not very high temperatures needed (under pyrolysis conditions), energetic gain, easily recoverable solvents, possibility of using a big number of solvents, extraction rate of about 90% of initial kerogen, etc. On the other hand, the most important disadvantage is the lack of thermodynamic equilibrium or solubility data available, mainly in multi component [13] . Shale oil also is produced by the thermal decomposition of its kerogen components. Oil shale must be heated to temperatures between 400˚C and 500˚C. This heating process is necessary to convert the embedded sediment to kerogen oil and combustible gases. Supercritical fluid extraction is the process of separating one component (the extractant) from another (the matrix) using supercritical fluids as the extracting solvent. Much research has been carried out on a small scale to develop extraction methods which operate at lower temperatures and which remove as much organic material from the shale as possible to maximize the oil yield. These include the use of supercritical, non-hydrogen donor solvents such as water, toluene and methanol. A wide range of hydrogen donor solvents have also been used including tetralin and hydrogenated recycle distillate [14] . Supercritical water extraction is receiving particular interest in oil shale processing due to the oil yield increase, ease of removal of the products, its compatiblity with the environment and its already accepted role as a means for shale oil processing for production of special chemicals like ethylene, propylene, benzene, toluene, and xylene [15] . The present study aimed to investigate the effect of different solvents on the extraction of shale oil from Egyptian oil shale obtained from Al-Quseir area for obtaining maximum yield of oil. Also it is aimed to study the effect of operating parameters including particle size, extraction time, stirring speed and solvent to oil shale ratio on rate of extraction.

Demand for light hydrocarbons has been steadily increasing in the market with a corresponding decrease in heavy hydrocarbon demand. Therefore, there is a need to develop environmentally friendly and efficient technologies for conversion of heavy molecular weight hydrocarbons. In the present study, the nature of solvent was found to have a very significant effect on the yield of recovery and the composition of the oils obtained. The oil yield obtained by THF extraction is significantly higher than those obtained by other solvents.