Crude petroleum possesses a very repugnant odor; it varies in color from yellow to black; and its specific gravity ranges from about 0.80 to 1.00, but commonly is between 0.80 and 0.90.  Its chemical constitution is chiefly of carbon and hydrogen, in the approximate ratio of about six to one respectively.  It is a mixture of paraffin hydrocarbons having the general formula of C_{n}H_{2n+2} and the individual members of this series vary from CH_{4} (methane) to C_{15}H_{32} (pentadecane), although the solid hydrocarbons are still more complex.  Petroleum is found in many countries and the United States is particularly blessed with great stores of it.

The ordinary lamp consisting of a wick which draws up the mineral oil and feeds it to a flame is efficient and fairly free from danger.  It requires care and may cause disaster if it is upset, but it has been blamed unjustly in many accidents.  A disadvantage of the kerosene lamp over electric lighting, for example, is the relatively greater possibility of accidents through the carelessness of the user.  This point is brought out in statistics of fire-insurance companies, which show that the fires caused by kerosene lamps are much more numerous than those from other methods of lighting.  If in a modern lamp of proper construction a close-fitting wick is used and the lamp is extinguished by turning down and blowing across the chimney, there is little danger in its use excepting accidental breakage or overturning.

In oil-lamps at the present time mineral oils are used which possess flashing-points above 75 deg.F.  The highly volatile components of petroleum are dangerous because they form very explosive mixtures with air at ordinary temperatures.  A mineral oil like kerosene, to be used with safety in lamps, should not be too volatile.  It is preferable that an inflammable vapor should not be given off at temperatures under 120 deg.F.  The oil must be of such physical characteristics as to be drawn up to the burner by capillarity from the reservoir which is situated below.  It is volatilized by the heat of the flame into a mixture of hydrogen and hydrocarbon gases and these are consumed under the heat of the process of consumption by the oxygen in the air.  The resulting products of this combustion, if it is complete, are carbon dioxide and water-vapor.  For each candle-power of light per hour about 0.24 cubic foot of carbon dioxide and 0.18 cubic foot of water-vapor are formed by a modern oil-lamp.  That an open flame devours something from the air is easily demonstrated by enclosing it in an air-tight space.  The flame gradually becomes feeble and smoky and finally goes out.  It will be noted that a burning lamp will vitiate the atmosphere of a closed room by consuming the oxygen and returning in its place carbon dioxide.  This is similar to the vitiation of the atmosphere by breathing persons and tests indicate that for each two candle-power emitted by a kerosene flame the vitiation is equal to that produced by one adult person.  Inasmuch as oil-lamps are ordinarily of 10 to 20 candle-power, it is seen that one lamp will consume as much oxygen as several persons.